production of materials - millennium schools production of materials chemical knowledge,...

Gill Sans Bold

CHEHSC43186 P0025953

ChemistryHSC CourseStage 6

Production of materials

Incorporating October 2002

AMENDMENTS

AcknowledgmentsThis publication is copyright Learning Materials Production, Open Training and Education Network –Distance Education, NSW Department of Education and Training, however it may contain material fromother sources which is not owned by Learning Materials Production. Learning Materials Productionwould like to acknowledge the following people and organisations whose material has been used.

• Chemistry Stage 6 Syllabus, Board of Studies NSW, Amended October 2002The most up-to-date version is to be found athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html

• Australian Nuclear Science and Technology Organisation, Lucas Heights

All reasonable efforts have been made to obtain copyright permissions. All claims will be settled ingood faith.

Writer: Richard Alliband

Editors: Michael Cutrupi (Trinity College, Auburn)

Julie Haeusler

Illustrator: Thomas Brown

Consultants: Sue Colman (OTEN-DE)

Professor Peter Rogers (Biotechnology, UNSW)

Format: Nick Loutkovsky

Copyright in this material is reserved to the Crown in the right of the State of New South Wales.Reproduction or transmittal in whole, or in part, other than in accordance with provisions of theCopyright Act, is prohibited without the written authority of Learning Materials Production.

© Learning Materials Production, Open Training and Education Network – Distance Education,NSW Department of Education and Training, 2000. Revised October 2002 51 Wentworth Rd.Strathfield NSW 2135.

Introduction i

Contents

Module overview ........................................................................iii

Indicative time...................................................................................... iv

Resources............................................................................................ iv

Icons ................................................................................................... vii

Additional resources........................................................................... vii

Glossary............................................................................................. viii

Part 1: Polymers from fossil fuels........................................ 1-32

Part 2: Polymers from biomass ........................................... 1-40

Part 3: Renewable ethanol .................................................. 1-32

Part 4: Galvanic cells – electrical energy from materials..... 1-41

Part 5: Nuclear chemistry ................................................... 1-26

Part 6: Review, report and outcomes .................................. 1-17

Student evaluation of module

ii Production of materials

Introduction iii

Module overview

The extracts below are from the Chemistry Stage 6 Syllabus ” Board of Studies

NSW, October 2002. The most up-to-date version is to be found athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html

'Humans have always exploited their natural environment for all theirneeds including food, clothing and shelter. As the culturaldevelopment of humans continued, they looked for a greater variety ofmaterials to cater for their needs.'

In the Preliminary module Metals you studied how important metalswere in the development of human cultures. For a society to progress toa bronze age or iron age based culture access was needed to suitableminerals and energy to extract the metals.

'The twentieth century saw an explosion in both the use of traditionalmaterials and in the research for development of a wider range ofmaterials to satisfy technological developments. Added to this was areduction in availability of the traditional resources to supply theincreasing world population.'

In the twentieth century materials based upon non-metals such as carbonand semi-metals such as silicon have revolutionised transportation andcommunication. Increasing affluence and the importance placed uponmaterial possessions and mobility have increased incentives to developalternative materials and energy sources.

'Chemists and chemical engineers continue to play a pivotal role in thesearch for new sources of traditional materials such as those from thepetrochemical industry. As the fossil organic reserves dwindle, newsources of the organic chemicals presently used have to be found. Inaddition, chemists are continually searching for compounds to be usedin the design and production of new materials to replace those thathave been deemed no longer satisfactory for needs.'

iv Production of materials

Chemical knowledge, understanding and skills have underpinned thedevelopment of silicon chips, optical fibres, solar cells, plastics,ceramics, new alloys and more efficient use of energy sources.

‘This module increases students’ understanding of the implications ofchemistry for society and the environment and the current issues,research and developments in chemistry.’

The emphasis in this module is on Prescribed Focus Areas 4 and 5.

Indicative time

This module is designed to take a minimum of thirty hours. There are anumber of practical activities. Organising materials and equipment forcarrying out all these activities could take additional time but in doing soyou will better understand the type of work chemists do.

Resources

Materials and equipment you need to carry out activities are listed below.Access to a computer and the world wide web are important for the studyof modern chemistry. An important skill to develop in chemistry isplanning ahead and thinking things through before carrying out theaction. Make sure the resources you need are available when you start anactivity. For details see the activity in the appropriate part.

For Part 1 you will require:

• an alkane eg. cyclohexane if you have access to a laboratory

• an alkene eg. cyclohexene if you have access to a laboratory

• bromine water in a dropper bottle, eye protection (glasses orgoggles) and access to a laboratory OR iodine tincture/iodine paint(purchased from a pharmacy) and a dropper bottle

• ten test tubes with stoppers

• food oils such as safflower, olive, peanut, etc.

• baby oil (or light liquid paraffin oil)

• tomato juice

• drinking straws or wooden skewers

• coloured pencils

• 3 transparent plastic bags and ties to seal the bags

Introduction v

• 8 transparent glass containers (eg. beakers/test tubes/petri dishes)

• 1 ripe and 1 green banana OR 1 ripe and 1 unripe apple OR ripe andunripe samples of other fruits

• an area where you can leave the 3 plastic bags and contentsundisturbed for a few days (away from pets and young children)

• molecular model kit OR Lego“ style blocks

OR jelly lollies (such as cut jelly snakes) and toothpicks

• ethanol or methylated spirits


• a stick of celery with a leafy top

• access to clean water

• some transparent adhesive tape and a piece of newspaper

• hand lens or magnifying glass

• tincture of iodine solution and a dropper bottle

• a glass or plastic container

• filter paper

• at least 1 m of metal wire (bare or plastic covered)

• means of cutting the metal wire eg. pliers

• plasticine or Blu-tack“

• molecular model kit OR Maltesers® and toothpicks and a red markerpen OR coloured jelly jubes/marshmallows and toothpicks

• methylated spirits

• household substances eg. some of the following: biro ink, bootpolish, candle wax, grease, oil, aspirin tablets, salt, sugar, gelatine orjelly crystals, vinegar, soap, glycerol


• a balance capable of weighing to at least the nearest gram

• a gas tight container with a tube passing to a smaller container

• 25 g glucose or sucrose (table sugar)

• 1 g table salt

• 7 g dried yeast (found in the bread making or flour section of asupermarket - usually in 7 g, 12 g or 28 g packets)

• limewater

• alcohol burner

vi Production of materials

• alkanols such as methanol, ethanol (or methylated spirits), propanol

• a means of measuring the mass of burner to at least 0.01 g ORa means of measuring the volume of alkanol used to 0.2 mL and adata source of alkanol densities

• 500 mL conical flask or empty aluminium drink can

• a thermometer measuring to at least 0.5 of a Celsius degree

• a box of matches

• a means of supporting the conical flask or empty aluminium drinkcan containing 250 mL of water about 5 cm above the top of theburner flame


• iron nail (if rusty, clean surface with iron wool)

• solution of copper(II) ions eg. copper(II) sulfate solution or asolution of copper(II) acetate prepared by dissolving coppercarbonate in vinegar; copper that has been exposed to theatmosphere (but not near salt water) for a long time can be coveredwith green carbonate

• small transparent container to hold the nail partly in and partly out ofthe solution

• finely divided zinc Zn(s); this can be obtained by shaking out powderfrom the bottom of a plastic bag that contained galvanised nails or byrunning a metal file down the side of a galvanised nail many times

• a dilute iodine solution I2(aq); prepared by adding one drop of iodinetincture to every two millilitres of water

• a small test tube to hold the iodine solution

• a variety of metals eg. steel paper clip, brass drawing pin, zincgalvanised nail, copper wire, silver plated cutlery, nickel platedjewellery.

• an electrolyte solution eg. a citrus fruit juice solution such as in alemon which has been rolled and massaged by hand to enable thecitric acid solution to move freely; cut the fruit in halfOR a solution of acid such as vinegar (5%w/w acetic acid solution)or a salt solution (make about 5%w/w salt) in a container

• to detect the current produced you will need a multimeter able tomeasure to at least 0.2 volts DC

• two small liquid containers in the range 50 - 300 mL.


• Internet access to complete Exercise 5.2.

Introduction vii

Icons

The following icons are used within this module. The meaning of eachicon is written beside it.

The hand icon means there is an activity for you to do.It may be an experiment or you may make something.

You need to use a computer for this activity.

Discuss ideas with someone else. You could speak withfamily or friends or anyone else who is available. Perhapsyou could telephone someone?

There is a safety issue that you need to consider.

There are suggested answers for the following questionsat the end of the part.

There is an exercise at the end of the part for you tocomplete.

You need to go outside or away from your deskfor this activity.

Additional resources• Morton, B. (1999.) Ethylene senior chemistry. Orica Limited.

• Anderson, A. (1998.) Polyethylene senior chemistry. OricaLimited.

• T P Lyons et al (Editors). (1995.) The alcohol textbook.Nottingham University Press.

• The nuclear source. ANSTO. (1992.)

viii Production of materials

Glossary

The following words, listed here with their meanings, are found in thelearning material in this module. They appear bolded the first time theyoccur in the learning material.

addition polymerisation polymer formation by adding together ofmonomer molecules containing C=C

addition reaction reaction in which at least two molecules addto produce a larger molecule

agrochemical chemical used in agriculture such as fertiliser,pesticide, herbicide

alcohol organic molecular substance with OH group

alkane CnH2n+2

alkanoic acid CnH2n+1COOH

alkanol CnH2n+1OH

alkene CnH2n or hydrocarbon containing C=C

alkyne CnH2n–2 or hydrocarbon containing carbon tocarbon triple bond

amide molecule containing NHCO; the linkagebetween monomers in polyamides like nylon

amino acid H2N–RCH–COOH where the R group varies

amorphous 'without structure'; non-crystalline

anhydrous without water

anode electrode at which oxidation occursmnemonic: AN OX

bioconversion conversion of one chemical to another by aliving thing

biodiesel diesel fuel from living things

bioethanol ethanol from cellulose in biomass

biogas combustible gas, usually methane, from livingthings

biomass organic matter produced by photosynthesis;mostly cellulose

biopolymer naturally occurring polymer generated usingrenewable resources like micro-organisms orplants; the organisms used may be geneticallymodified

Introduction ix

button cell button shaped electrochemical cell

catalyst substance which speeds up a chemicalreaction and remains unchanged at the end ofthe reaction

catalytic involving a catalyst

catalytic cracking cracking large hydrocarbon molecules tosmall hydrocarbon molecules with hotcatalyst

cathode electrode at which reduction occursmnemonic: RED CAT (reduction at thecathode)

cellulase enzyme or group of enzymes that changecellulose to glucose

cellulose polymer of b-glucose

CFCs chlorofluorocarbons

chain reaction a sequence of self-sustaining reactions;important in polymerisation and nuclearfission

chemotherapy treatment using chemicals

condensation polymer polymer formed by monomer moleculescondensing out a small molecule

copolymer polymer made from more than one monomer

cracking breaking a large molecule into smallermolecules

crystallinity proportion of polymer that is in crystal(regularly arranged) form

cyclotron compact accelerator that sends chargedparticles in a spiral path

decay change to something simpler; radioactivedecay occurs spontaneously producing anucleus with fewer nucleons or a nucleus withless energy

delocalised electrons electrons that move between atoms in amolecule or structure

dehydration loss of water

denatured deprived of its nature; ethanol, is madeunpalatable for drinking by the addition ofpoisonous and bitter substances

x Production of materials

diesel engine internal combustion engine that ignites an oilfuel by compression

dry cell cell where electrolyte is paste or liquidabsorbed in a porous medium

electrode metal or graphite which transfers electrons inor out of an electrolyte

electrolysis chemical reaction caused by electrical energy

electrolyte liquid substance or solution through whichions can move

enhanced greenhouseeffect

increase over the Earth's natural greenhouseeffect as a result of human activity releasingextra gases eg. CO2, CH4, N2O, CFCs

enzyme biological catalyst

extrapolate estimate a quantity by extending beyond therange of measured data

feedstock raw materials for production

fermentation controlled chemical changed catalysed byenzymes from organisms such as yeast

fission products products of fission of a nucleus to smallerparts

flammable easily set on fire

fossil fuel fuel formed from the remains of plants oranimals which lived millions of years ago

free radical atom or molecule with a lone (unpaired)electron; very reactive

fuel substance that undergoes a change releasinguseful energy

fuel cell cell releasing electrical energy in which aflow of fuel is oxidised without burning

galvanic cell electrochemical cell capable of releasingelectrical energy from chemical energy

genetic engineering;genetic modification;genetic manipulation

alteration of the genes in chromosomes ofcells to attempt to change the capabilities ofoffspring

Gratzel cell liquid junction photovoltaic device

half equation equation showing oxidation or reduction

half-life time required for radioactivity level to halve

heat of combustion heat change when a substance is combusted

Introduction xi

HDPE high density polyethene

hydration addition of water

intermediate in between; a chemical species formedbetween reactant(s) and product(s)

internal combustionengine

engine that combusts fuel in a chamber torelease moving energy

ionising radiation electromagnetic (UV, X-rays) oralpha/beta/gamma radiation capable ofionising atoms to positive ions and electrons

isotopes atoms of the same element; they have thesame atomic no. but different mass numbers

LDPE low density polyethene

lead-acid cell electrochemical cell consisting of a lead plateand a lead oxide plate in concentrated sulfuricacid

liquid junctionphotovoltaic device

cell changing light energy absorbed by aliquid junction between anode and cathode toelectrical energy

lithium cell galvanic cell containing lithium and havinghigh energy output per kg eg. Li-FeS2 1.5 Vnon-rechargeable or Li-MnO2 rechargeable

LPG liquefied petroleum gas; a low pollution fuelfor internal combustion engines

lyophilic fat loving; non-polar substance

metabolic engineering transfer of genes for a metabolic pathwayfrom one organism to another

metabolic pathway pathway used by an organism to carry out achemical change; catalysed by enzyme(s)

methanogen 'methane former'; bacteria that make methane

mnemonic assisting the memory

molecular model kit kit consisting of plastic pieces that can bejoined together to represent the atoms andbonds in a molecule

monomer compound with small molecules able to jointogether to form long chain polymer molecule

mono-unsaturated molecule with one unsaturated group C=C

non-degradable unable to be decomposed naturally by decaybacteria or fungi

xii Production of materials

non-ionising radiation low energy radioactivity that has enoughenergy to excite electrons to higher energylevels but insufficient energy to ionise atoms

non-renewable resource that is available in fixed amount andcould be used up completely eg. petroleum

nuclear fission division of a nucleus into two unequal massesreleasing neutrons, gamma rays and massiveamounts of energy

nuclear reactor equipment for releasing nuclear energy slowlyin a usable form

nucleon particle in a nucleus; proton or neutron

organometallic compound containing an organic part and ametal

oxidant oxidising agent; chemical species that causesoxidation (loss of electrons)

oxidation state =oxidation number

number that increases on oxidation anddecreases on reduction

particle accelerator device for accelerating charged particles

PE polyethylene = polyethene = polythene

peptide linkage NHCO in proteins between amino acids

PET polyethylene terephthalate plastic used tomake recyclable soft drink bottles; positron-emission tomography technique for imagingthe brain using radioisotopes made in acyclotron

petranol mixture of petrol and alcohol

petrochemical chemical made from compounds in petroleum

photovoltaic light energy to electrical energy eg. as insilicon solar or liquid junction Gratzel cell

plasticiser chemical the molecules of which fit betweenpolymer chains increasing flexibility

polyethylene polymer of ethylene

polymer long chain molecule formed by joiningmonomer molecules

polyunsaturated molecule with more than one C=C group

potential potential difference or voltage measured in V

PP polypropylene, polymer of propeneCH3CH=CH2

Introduction xiii

PPVC plasticiser added PVC that is more flexible

PS polystyrene

PVC poly(viny lchloride)

radioactive isotope radioisotope

radioisotope radioactive isotope

radionuclide radioactive nuclide = radioisotope

reaction mechanism how reactants change in producing products

redox abbreviation of reduction-oxidation

reductant reducing agent; chemical species that causesreduction (gain of electrons )

reduction gain of electrons by a chemical species

renewable resource that can be used then reformed fromproducts by input of solar energy

saturated carbon compound saturated with hydrogencontaining C–C bonds and no double or triplebonds

steam cracking cracking by mixing with steam and passingthrough hot coils

surface reaction reaction occurring on the surface of a solid

thermoplastic polymer material that can be melted by heat(thermo) and shaped (plastic)

tincture aqueous alcohol solution

tracers radioisotopes used to signal passage of anatom through a system

transuranic element with an atomic number above 92,beyond uranium

UPVC unplasticised PVC; rigid PVC

V PVC abbreviation for recyclable material

zeolites aluminium silicates; different types are usedas catalysts, molecular sieves and separators

Gill Sans Bold



Part 1: Polymers from fossil fuels


AMENDMENTS

Common namesof monomer

Systematic nameof monomer

Polymer usesRecyclableplastic symbol

ethylene ethenebags, water pipes,gas pipes, buckets,bottles, garbage bins

2 HDPE

4 LDPE

vinyl chloride,chloroethylene

chloroethene

garden hoses, shoesoles, conduit, wastewater pipes, creditcards, floor tiles

3 V or PVC

styrene,vinyl benzene,phenyl ethene

ethenylbenzeneplastic cutlery, brittletoys, CD cases, bikehelmet padding

6 PS

Part 1: Polymers from fossil fuels 1

Contents

Introduction ............................................................................... 2

Reactivities of alkenes and alkanes .......................................... 4

Ethylene, leaves and bananas ..........................................................11

Fuel or raw material?............................................................... 13

Ethylene production ...........................................................................15

Useful products from ethylene...........................................................15

Monomers and polymers......................................................... 17

Addition polymerisation......................................................................17

Polymers.............................................................................................18

Production of polyethylene ...............................................................19

Investigating LDPE and HDPE..........................................................21

Properties and polymer structures ....................................................23

Suggested answers................................................................. 25

Exercises – Part 1 ................................................................... 29

2 Production of materials

Introduction

Fossil fuels provided the energy that has fuelled a marked increase in theworld’s population over the last two hundred years. In the last centuryfossil fuels have also become increasingly important in providing rawmaterials such as ethylene to make useful materials like the additionpolymers polyethylene, poly(vinyl chloride) and polystyrene.

In Part 1 you will be given opportunities to learn to:

• identify the industrial source of ethylene from the cracking of someof the fractions from the refining of petroleum

• identify that ethylene, because of the high reactivity of its doublebond is readily transformed into many useful products

• identify that ethylene serves as a monomer from which polymers aremade

• identify polyethylene as an addition polymer and explain themeaning of this term

• outline the steps in the production of polyethylene as an example ofa commercially and industrially important polymer

• identify the following as commercially significant monomers:

– vinyl chloride

– styrene

by both their systematic and common names

• describe the uses of the polymers made from the above monomers interms of their properties.

In Part 1 you will be given opportunities to:

• gather and present information from first-hand or secondary sourcesto write equations to represent all chemical reactions encountered

• identify data, plan and perform a first-hand investigation to comparethe reactivities of appropriate alkenes with the corresponding alkanesin bromine water


• analyse information from secondary sources such as computersimulations, molecular model kits or multimedia resources to modelthe polymerisation process.

Extracts from Chemistry Stage 6 Syllabus ” Board of Studies NSW, October

2002. The most up-to-date version can be found on the Board’s website athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html


MACRO MICROSYMBOLICparticles

energyinteractions

H2O

MACRO MICROSYMBOLICobserveinferunderstand

formulasequations

calculations

particlesenergy

interactions

observeinferunderstand

formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Reactivities of alkenes and alkanes

Three activities are listed below comparing reactions of alkenes andalkanes or studying reactions of compounds containing the carbon tocarbon double bonds, C=C, found in alkenes. The first and thirdactivities that involve bromine water should only be carried out inlaboratory conditions. The second and third activity involving iodinesolution can be safely carried out at home.

Special care is needed if using bromine water. It is a corrosive solution, askin irritant and releases irritant vapour. Use a fume cupboard wheneverpossible, otherwise use small quantities in a well ventilated area.

Bromine water can be prepared by opening or carefully breaking a glassampoule of 2 mL of liquid bromine at the bottom of a container of 400 mLof water in a fume cupboard. Dissolution of all the bromine prepares a0.1 M solution. The 400 mL should be divided into two lots and stored inwell sealed containers. Bromine water loses bromine to the air and changesconcentration whenever the container lid is removed. One lot of brominewater should be used first. Comparison of the intensity of its colour with anequal volume from the second sealed lot will give an approximate idea ofany decrease in concentration.

When not in use the bromine solution must be kept in a well sealedcontainer, preferably within a larger sealed container, in a refrigerator (not afreezer). The 0.1 M solution should be diluted to about 0.01 M for use bystudents. A small dropper bottle provides convenient access. Students mustwear eye protection (glasses or goggles) when using bromine solution.

Iodine solution is less hazardous and can be prepared from iodinetincture (2.5% iodine w/v, approximately 0.1 M) or iodine paint (5%iodine w/v, approximately 0.2 M) which can be purchased at pharmacies($3-5 for 50 mL). The purchased solutions contain iodine dissolved inaqueous alcohol. Before use the solutions must be diluted to about 0.1%iodine w/v solution. One drop of iodine tincture to each millilitre ofwater or one drop of iodine paint to every 2 mL of water will produceabout 0.1% iodine w/v solution. This iodine solution is about 0.004 M.Store the 0.1% iodine w/v solutions in a sealed container in a refrigerator.


Activity 1: Reactivity of cyclohexane and cyclohexene with brominewater. This activity requires access to a supervised laboratory.

Cyclohexane and cyclohexene are highly flammable and release moderatelytoxic vapour. Wear eye protection especially when using bromine water.

What you will need:

• two glass test tubes or small beakers

• cyclohexane

• cyclohexene

• 0.01 M bromine water in a dropper bottle.

What you will do:

1 Add about 1 mL (about twenty drops) of cyclohexane to onecontainer and about 1 mL of cyclohexene to the other container.Fill your lungs with air then gently wave your hand over the top of acontainer towards your nose. Take a short sniff of air containing thevapour into your nose then breathe much more air from your lungsout through your nose. Repeat for the other container. Note theodour difference.

2 Add an equal volume of bromine water to each of the liquids thenshake each container to the same extent.

How to hold a test tube and shake its contents


3 Leave the containers to settle, then observe.

4 Use your observations and data in the table below to recordobservations and conclusions.

Properties Cyclohexane Cyclohexene

odour

density (g cm–3) 0.77 0.81

colour before addition ofbromine water

colour after shaking withbromine water

colour of bromine waterbefore addition

colour of water layerafter shaking

If you think about your observations you will probably conclude that thealkane did not react whereas the alkene did react with the bromine.Alkene removes bromine from its water solution.

1 Which observation(s) can be interpreted as showing that bromine hasreacted with the alkene?

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 What happens to the colour of bromine water when the brominereacts?

______________________________________________________

Check your answers.

The reactive C=C in alkenes can react with bromine:

\ / Br2 \ / C = C Æ Br – C – C – Br/ \ / \

The compound formed is a 1,2-dibromoalkane. Cyclohexene forms1,2-dibromocyclohexane. Because two molecules (bromine and


cyclohexene) add to give a single molecule (1,2-dibromocyclohexane)the reaction is called an addition reaction. Note that the double bond haschanged to a single bond as two of the electrons in the double bond wereneeded to form covalent bonds with the two bromine atoms added.

If the bromine is in water solution a hydroxy group –OH and a bromineatom –Br can be added to the carbons associated with the double bond.

\ / Br2, HOH \ / C = C Æ Br – C – C – OH/ \ / \

The compound formed is a 1-bromo-2-hydroxyalkane. Cyclohexeneforms 1-bromo-2-hydroxycyclohexane in which there is no double bond.

Activity 2: Reactivity of iodine water with food oils

What you will need:

• approximately 0.1% iodine water (made by adding a drop of iodinetincture to each millilitre of water used) in a dropper bottle

• test tubes with stoppers

• at least two different food oils

• baby oil (or light liquid paraffin oil).

Background information

Food oils such as safflower, olive, peanut, etc. have varying amounts ofunsaturation. If each hydrocarbon chain is saturated with hydrogen, thatis only has C – C bonds, then the oil is called a saturated oil. If an oilmolecule has one C = C the oil is mono-unsaturated. When there ismore than one C = C per molecule the oil is called polyunsaturated.A balanced diet should include all three types of oils.

You can determine which oils are most unsaturated by comparing theamount of iodine that reacts when the oils are shaken with iodine water.

Many food oils are coloured yellow, the same colour as dilute iodinewater. To make change easier to see you will shake the iodine waterwith baby oil. When the non-polar iodine molecules transfer from thepolar water layer to the non-polar baby oil layer the iodine appears aviolet colour.

When shaken together vigorously oil and water will tend to form a whiteemulsion. An emulsion is a suspension of small droplets of one liquid inanother liquid. An emulsion is white because the surface of the smalldroplets reflect light. If you wait five minutes the emulsion should


separate into two layers. This separation enables you to see any colour inthe more dense, polar, water layer and the less dense, non-polar, oil layer.

To test a food oil for unsaturation:

1 Add some iodine water to the test tube.

2 Add about half the iodine water volume of baby oil, stopper the testtube and shake vigorously up and down for ten seconds. The yellowto violet colour change is due to a physical change as non-polariodine moves from water to non-polar oil.

3 Add food oil, stopper the test tube and shake vigorously up anddown for ten seconds. If the violet colour disappears the iodine hasreacted with unsaturated groups in that food oil.

The loss of violet colour is due to a chemical change as iodinedisappears reacting chemically with –C=C– to form –C–C– | | I I

In the space below plan a first-hand investigation to compare the amount ofsaturation in at least two different food oils. Perform your investigation andwrite a report that includes aim, method, results and a conclusion.Remember to use labelled diagrams and tables where relevant.


Activity 3: Tomato juice rainbow using bromine water or iodine water

What you will need:

• tomato juice (normally contains about 20 mg of lycopene per mL)

• about ten transparent containers (test tubes or beakers)

• bromine water or iodine water in dropper bottles

• drinking straws—NOT to be used for drinking—or wooden skewersto stir the tomato juice with the bromine water or iodine water

• coloured pencils.

Don’t forget your eye protection whenever using bromine water. The resultswith bromine water are usually more colourful than with iodine water.

Background information:

Tomato juice, watermelon and pink grapefruit contain a red colouredplant chemical (phytochemical) called lycopene. Lycopene is ahydrocarbon C40H56 with the following structure:

C

CH3

H3C CH

H2C

C H2

C

CH3

CH

HC

CH

C

CH3

CH

HC

CH

C

CH3

CH

HC

CH

C

HC

CH3

HC

CH

C

CH3

HC

CH

C

CH3

HC

C H2

C

CH3

HC

HC

H2C CH3

or more simply drawn as:

Lycopene is an antioxidant, able to neutralise harmful reactive substancesin the body called free radicals. There is evidence that a diet high inlycopene reduces the incidence of heart attacks and certain cancers suchas prostate cancer. Cooking tomatoes provide more lycopene becausethe heat breaks down tomato cell walls, freeing the lycopene.

The alternating double and single bonds in lycopene provide delocalisedelectrons that can move freely from carbon atom to carbon atom.Most carbon compounds are colourless but a compound such as lycopenewith lots of delocalised electrons in a long chain can absorb parts ofvisible light. The colour of a compound is the colour of the light that isnot absorbed, that is the colour that is reflected or transmitted toyour eye.

Lycopene crystals are a tomato red colour. Tomato juice containinglycopene is red.


Which colour of visible light is not absorbed by lycopene?

_________________________________________________________

What you will do:

1 Place about 5 mL of tomato juice in the ten test tubes/small beakers.

2 Add varying amounts of bromine water or iodine water to eachcontainer. Experiment with different amounts to try and produce arange of colours.

It is possible, but difficult, to produce the range of visible spectrumcolours red (unreacted tomato juice), orange, yellow, green and blue.

3 Draw what you see using the coloured pencils. Provide informativelabels to show the amounts of tomato juice and bromine or iodinewater used.

Explain what you have observed in terms of possible reactions of lycopenewith bromine or iodine and changes in the structure of lycopene.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.


Ethylene, leaves and bananas

Towards the end of the 1800s it was noticed that trees near street lampsin a German city lost their leaves unexpectedly. Investigations showedthat ethylene in leaking gas used to fuel the street lamps was responsible.Ethylene was also found to be given off by ripening fruit and acted as aplant hormone. Today ethylene at about 10 ppm concentration is used toripen and colour bananas, pears, mangoes, tomatoes and citrus, to induceflowering in pineapple plants and to improve the growth and appearanceof bean sprouts.

Note that ethylene is the IUPAC name for C2H4. Ethene is the systematicname for C2H4 but ethylene is the IUPAC preferred name.

Investigating ethylene

You will need:

• 3 transparent plastic bags and ties to seal the bags

• 8 transparent glass containers (eg. beakers/test tubes/petri dishes)

• 12 mL of diluted (about 0.01M) bromine water and eye protection(glasses or goggles) and/or

12 mL diluted iodine solution made by adding 12 drops of 2.5% w/viodine tincture to 12 mL of water

[If you do not have access to diluted bromine or iodine you could trya very dilute solution of potassium permanganate KMnO4 solutionwhich is a light purple colour. KMnO4 crystals can be purchased atpharmacies as Condy’s crystals. KMnO4 is one of the most intenselycoloured chemicals known – only a small crystal is needed toprepare a solution and that solution may need to be diluted to get alight purple colour.]

• 1 ripe banana and 1 unripe banana OR 1 ripe apple and 1 unripeapple OR ripe and unripe samples of other fruits

• an area where you can leave the 3 plastic bags and contentsundisturbed for a few days (away from pets and young children).

What you will do:

1 Into each of three bags as well as the area where the bags are to bekept place:

– 3 mL diluted bromine water in an open container and/or

– 3 mL diluted iodine solution in an open container.

2 To a bag labelled R add a ripe banana/apple/fruit.


3 To a bag labelled U add an unripe banana/apple/fruit.

4 No banana or apple goes into the bag labelled N.

5 Seal each bag with a tie then place the three bags in the same area.Make sure the bags are not exposed to direct sunlight or heat. Thebags should contain about the same amount of air each.

6 Observe the three transparent bags over the next three days and noteany changes in their contents.

1 Why was diluted bromine or iodine solution placed in the area nearwhere the plastic bags were kept?

_____________________________________________________

_____________________________________________________

______________________________________________________

2 Why was no banana/apple/fruit placed in one of the bags?

______________________________________________________

______________________________________________________

______________________________________________________

3 Can you come to some conclusions from your observations?

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Fuel or raw material?

Some projections of current rates of use of Australian fossil fuels basedupon known reserves indicate the availability of:

• coal supplies for about 1000 years

• natural gas supplies for about 100 years

• petroleum supplies for about 10 years.

There are ways of converting the more plentiful solid coal to liquid fuelssuch as compressed natural gas and petrol but at costs to theenvironment. The conversion methods can produce considerable wasteand do not overcome the enhanced greenhouse effect. Burning thecarbon that has been trapped for millions of years in any fossil fuelincreases carbon dioxide levels in the global atmosphere. Carbondioxide is not considered a pollutant locally but it is globally. Higherconcentrations of carbon dioxide trap more heat within the atmosphereand are believed to raise average temperatures globally.

Earth

Some solar radiation isreflected by the Earth’ssurface and theatmosphere

atmosphere

Most solar radiationis absorbed by theEarth’s surface

Some of the infra-redradiation from the Earth’ssurface is absorbed andre-emitted by enhancedgreenhouse gases suchas CO2, CH4, N2O andCFCs. This re-emissionof infra-red radiationraises the temperature ofthe lower atmosphere andthe Earth’s surface.

Longer wavelength infra-redradiation is emitted from theEarth’s surface

Light andshortwavelengthinfra-redradiationpassesthrough theatmosphere

Sun


The carbon compounds in coal, natural gas and petroleum up to thepresent time have mostly been used as fuels – burnt in air as a source ofheat energy. Because supplies are limited and carbon compounds are soimportant in making synthetic rubbers, synthetic textile fibres, plastics,paints, detergents, pharmaceuticals, cosmetics, herbicides, pesticides,agricultural chemicals and so on, the use of fossil fuels as fuels–burntand lost for ever–is increasingly questioned.

A wiser use that would benefit many more humans for many moregenerations would be to use fossil ‘fuels’ as raw materials only.This requires alternative methods of making energy available such as thebiomass to ethanol and electrochemical and nuclear methods. You willcover these in Parts 3 to 5 of this module.

Petroleum is regarded as the most valuable of fossil fuels because of itsgreater diversity of compounds compared with natural gas or coal.Petrochemicals are chemicals made from compounds in petroleum.However the main use for over 90% of petroleum hydrocarbonsconsumed worldwide is still as fuel, burnt and lost forever.

Consider the C1 to C8 alkanes. Complete the first and second columns ofthe table. Do you remember the general formula for alkanes? CnH2n+2.

Alkane Formula Use

methane CH4 natural gas

ethane C2H6 petrochemical

propane liquefied petroleum gas (LPG)

C4H10 liquefied petroleum gas (LPG)

pentane petrol used in cold climates

C6H14 petrol used in cold climates

heptane petrol

octane petrol

Which one of the C1 to C8 alkanes is too valuable to use as a fuel?

Ethane C2H6 is too valuable to use as a fuel as it can easily be changedinto ethylene C2H4, the petrochemical used in greatest amount formaking plastics.


Ethylene production

Ethane gas can be converted to ethylene gas by cracking–breaking largermolecules (eg. ethane) into smaller molecules (ethylene and hydrogen).

C2H6(g) + heat Æ C2H4(g) + H2(g)

Cracking is endothermic because a molecule has to be broken apart intosmaller molecules. Energy is absorbed in breaking bonds to crack themolecule into smaller parts.

The hydrogen by-product can be used for other reactions such aschanging polyunsaturated liquid food oils (such as sunflower seed oil)into partly saturated solid fats (such as margarine).

There are two main sources of ethylene:

• as a by-product of the catalytic cracking of low value petroleumrefining fractions to high value petrol; the low value hydrocarbonsare passed over a solid heated catalyst.

• as the main product in steam cracking of ethane or low valuepetroleum refining fractions; ethane gas is mixed with steam andpassed into hot metal coils.

Complete Exercise 1.1: Petroleum fractions cracked to ethene.

Useful products from ethylene

Ethylene, because of the high reactivity of its double bond, reacts to formmany useful products such as polyethylene. Other chemicals whichcontain reactive double bonds are:

• styrene which reacts to form polystyrene

• vinyl chloride which forms poly(vinyl chloride).

Note: Just as ethylene is commonly called ethene, polyethylene iscommonly called polyethene or abbreviated to polythene.


1 Rewrite the equation C2H6(g) Æ C2H4(g) + H2(g) using structuralformulas.

2 At Orica’s Botany Bay ethylene production plant, each 1000 t of ethaneproduces about 780 t of ethylene.

a) Using the mole concept and molecular masses calculate the amountof hydrogen you would expect produced with each 780 t ofethylene.

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

b) Most reactions involving carbon compounds do not give all of thedesired products. As well as ethylene and hydrogen what mass ofother substances would you expect produced from each 1000 t ofethane?

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

Check your answers.

Complete Exercise 1.2: Products from ethylene.


Monomers and polymers

Monomers are small molecules able to join together to form long chainmolecules called polymers. When the small monomer molecules addtogether to form the polymer and no other product the reaction iscalled addition polymerisation. If the polymer name is written aspolyethylene then ethylene is the monomer and polyethylene isthe polymer.

Addition polymerisation

When an alkene monomer polymerises the double bonds change to singlebonds. Two of the electrons originally in each double bond are used tolink the carbon atoms together into long thin linear chains.

n(CH2=CH2) Æ CH —CH —CH —CH —CH —CH2 2 2 2 2 2 etc.

n = a large number (—CH —CH )2 2 n-

n units of monomer Æ polymer made of n monomer units

Polyethylene is used for plastic bags, clingwrap and black water pipes.

What you will need:

• molecular model kit or

• jelly lollies (such as cut jelly snakes) and toothpicks or

• Lego® style blocks.

What you do:

1 Make up at least four models of ethylene C2H4

2 Join the models together to make part of a polyethylene molecule(C2H4)n. Notice that the reactive double bonds are changed to morestable single bonds as the molecules join up.


Polymers

Monomers that undergo addition polymerisation usually have thestructure H H \ / C = C / \ H Z where Z can vary in different substances.

What does Z represent in ethylene? ____________________________

Check your answer.

Examples: H H \ / C = C / \ H Cl vinyl chloride Æ poly(vinyl chloride) PVC

æCH2æCHæCH2æCHæ | | Cl Cl H H \ / C = C / \ H C6H5 styrene Æ polystyrene

æCH2æCHæCH2æCHæ | | C6H5 represents a ring of six carbons C6H5 C6H5

with five attached hydrogens.

These monomers are commercially significant as they are used in largequantities to produce polymers.

Production of polyethylene

Varying production conditions and catalysts can produce differentpolyethylene molecules. Polyethylene molecules of different sizes anddifferent amounts of branching will have different properties andtherefore different uses. The two main types of polyethyleneproduced are:


• relatively soft low density polyethylene (LDPE) composed oftangled chains with molecular masses of less than 100 000

• harder high density polyethylene (HDPE) composed of alignedchains with molecular masses above 100 000.

Low density polyethylene LDPE is made by subjecting ethylene to highpressures. The reaction is initiated by a peroxide containing a O – Obond which breaks easily on heating producing two free radicals. A freeradical is an atom or molecule with a lone (unpaired) electron.The unpaired electron makes the free radical very reactive. When a freeradical joins onto an ethylene molecule the ethylene free radicalproduced becomes reactive.

Initiation

C6H5 C O O C

O O

C6H5 2C6H5 C

O

O

C6H5 C

O

OC

O

O = In In + C CH

H

H

HIn C C

H

H

H

H

Growth occurs by an ethylene free radical adding on other ethylenemolecules. The growth stage is called propagation.

Propagation

+ C CH

H

H

HIn C C

H

H

H

HIn C C

H

H

H

HC

H

H

C

H

H

The chain of ethylenes grows until this free radical ethylene chaincombines with another free radical ethylene chain to form a completepolyethylene molecule. Combination of the two free radicals is calledtermination because the pairing up of their two unpaired electrons meansthat the two free radicals no longer exist, that is, termination occurs.

Termination

In (CH2)n + (CH2)m In In (CH2) Inn+m

n+m typically 30 000 for LDPE

High pressure conditions with many molecule collisions produces shortbranches along the length of the LDPE chain.


= C and attached Hs

High density polyethene HDPE is made at low pressures. The catalystsused enable a more ordered orientation of reacting ethylenes producingvery long unbranched molecules.

= C and attached Hs

Industry and chemists usually refer to monomers by their common namesbut these names cannot always be used to predict the formula.A systematic name enables a person familiar with systematicnomenclature to predict the formula. Recycling code symbols appear onmany objects made of polyethylene, PVC and polystyrene.

Common namesof monomer

Systematic nameof monomer

Polymer uses Recyclableplastic symbol

ethylene ethene bags, water pipes,gas pipes, buckets,bottles, garbage bins

2 HDPE

4 LDPE

vinyl chloride,chloroethylene

chloroethene garden hoses, shoesoles, conduit, wastewater pipes, creditcards, floor tiles

3 V or PVC

styrene,vinyl benzene,phenyl ethene

ethenylbenzene plastic cutlery, brittletoys, CD cases, bikehelmet padding

6 PS


The monomers may be gases or liquids but the addition polymers areall solids because they are larger molecules with significantdispersion forces.

The bonding within the molecules are strong covalent bonds but the longthin molecules are held together by weaker dispersion forces.When heated the weaker dispersion forces are overcome and themolecules can flow into new shapes.

These addition polymers are called thermoplastics because they areeasily melted and shaped.

Investigating LDPE and HDPE

In 2000 nearly 10 kg of polyethylene (PE) was produced per person onEarth. The weight of polyethylene produced each year is greater than theweight of all other plastics. In most countries the weight of (cheap)polyethylene used is greater than the combined weight of all otherplastics used in that country.

Distinguishing between LDPE and HDPE

What you will need:

• LDPE eg. plastic food bag, anything with recycling code 4

• HDPE eg. plastic milk container, anything with recycling code 2

• Some fruit juice/milk containers have a HDPE body and a LDPE lid

• a 2/3 water and 1/3 ethanol (or methylated spirits) liquid mixture with adensity of approximately 0.94 g cm–3.

Push the plastic below the liquid surface wiping off any attached air bubbles.

1 Why does LDPE float while HDPE sinks? Answer this question at themicro level (that is, in terms of particles) and at the macro level (that is,in terms of a property of the material).

_____________________________________________________

______________________________________________________

_____________________________________________________

2 Predict which type of chain would pack together most closely andform crystals (regular arrangements) most easily.


3 Would this closer packing produce LDPE or HDPE?

4 Which structure would produce a softer, more flexible plastic forwrapping around and containing food?

5 Which structure would produce a harder, rigid plastic suitable forbuckets and plastic rulers?

6 Using simple diagrams to represent micro level structures ofpolyethylene explain why LDPE floats while HDPE sinks in themixture of water and ethanol.

7 List objects in your home that are made from LDPE and objects thatare made from HDPE.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

8 The amount of polymer in crystal form determines its crystallinity.Most polymers are a mixture of crystalline regions where themolecules are aligned and non-crystalline (amorphous) regionswhere the molecules are tangled.

crystallinenon-crystalline (amorphous)


Crystalline region Non-crystalline region

opaque transparent

higher MP lower MP

rigid flexible

low permeability to gases permeable to gases

Which form of PE has the greatest crystallinity – LDPE or HDPE?

_____________________________________________________

Check your answers.

You should now be able to explain the different properties of LDPE andHDPE using models of how the molecules are arranged.

Properties and polymer structures

The properties of a polymer are determined by the polymer structure andsize of the polymer molecules. The greater rigidity of poly(vinylchloride) (PVC) and polystyrene (PS) compared with polyethene (PE) ispartly due to the bulkier Cl and C6H5 groups compared with H in the PEpolymer structure. Larger molecular size as well as greater crystallinityproduce less flexibility, greater hardness and higher MP in HDPEcompared with LDPE. These different structures can be used to explainwhy HDPE plastic bags are crinkly while LDPE plastic bags are softerand tear more easily.

Poly(vinyl chloride) is often marked UPVC or PPVC depending onwhether the PVC is unplasticised or plasticised. Plasticisers aremolecules which fit between polymer chains and reduce dispersionforces. The addition of plasticisers makes PPVC much more flexiblethan UPVC.

= plasticiser

PVC is water resistant. It is used for raincoats, shower curtains andwaste water pipes. PVC is also flame resistant – when PVC is heated itreleases chlorine atoms which inhibit combustion reactions.


In polystyrene the bulky C6H5 groups both increase dispersion forces andinhibit large crystal formation. The low crystallinity makes polystyrenetransparent and suitable for clear plastic drinking glasses and CD(compact disk) cases. If polystyrene absorbs liquid pentane and is heatedto 36°C the pentane boils and changes to gas. This expands thepolystyrene forming a white material of very low density. The expandedpolystyrene formed is called polystyrene foam. It is a good heat insulatorand used for hot drink cups as well as packaging material and shockabsorber inside bike helmets.

Complete Exercise 1.3: Fossil fuel products.


Suggested answers

Activity 1: Reactivity with bromine water

Properties Cyclohexane Cyclohexene

odour mild strong

density (g cm–3) 0.77 0.81

colour before addition ofbromine water

colourless colourless

colour after shaking withbromine water

colourless colourless

colour of bromine waterbefore addition

yellow yellow

colour of water layerafter shaking

yellow colourless

1 The change in colour of bromine water from yellow to colourlesswhen shaken with cyclohexane indicates reaction. The observationthat cyclohexane did not affect the colour of the bromine watersuggests no reaction has occurred.

2 Bromine water changes from yellow to colourless as the yellowbromine reacts.

Activity 2: Reactivity of iodine water with food oils

Aim:

To compare the amount of saturation in olive oil and peanut oil byreaction with iodine water.


Method:

1 Add an equal amount of iodine water to the two test tubes.

2 Add about half the iodine water volume of baby oil, stopper the testtubes and shake vigorously up and down for ten seconds.

3 Add two drops each of olive oil and peanut oil to the separate testtubes; stopper and shake in the same way then compare colours.

4 If no colour change add a further two drops of oil to each test tubeand repeat shaking.

Result:

The test tube containing olive oil was the first to lose its violet colour.

Conclusion:

Olive oil reacted with iodine more quickly than peanut oil. Olive oiltherefore contains more unsaturated hydrocarbon than peanut oil.

Activity 3: Tomato juice rainbow

Red light is not absorbed by lycopene.

Bromine or iodine atoms can add to any carbons joined by double bondschanging the bonds between the carbons to single bonds. The removal ofdouble bonds and their delocalised electrons (used to attach thebromine/iodine atoms) affects the parts of visible light that are absorbed.As more bromine/iodine atoms add to a lycopene molecule the coloursabsorbed, and therefore the colour reflected by a solid or transmitted by asolution, changes.

Ethylene, leaves and bananas1 Dilute solutions of bromine/iodine were kept as a control – to see the

rate at which other substances in the air react with bromine/iodine orthe rate at which bromine/iodine escape from the solution into air.

2 No fruit was placed in one of the bags as a control eg. to see ifchemicals released by the plastic bag affected the bromine/iodinesolution.

3 Results will depend on the stage of ripeness of fruit, temperature,and so on. As the banana/apple/fruit ripens ethylene may be releasedand react with the bromine/iodine decolourising the solution.


Fuel or raw material?

Alkane Formula Use

methane CH4 natural gas

ethane C2H6 petrochemical

propane C3H8 liquefied petroleum gas (LPG)

butane C4H10 liquefied petroleum gas (LPG)

pentane C5H12 petrol used in cold climates

hexane C6H14 petrol used in cold climates

heptane C7H16 petrol

octane C8H18 petrol

1 H H H H | | \ /H– C – C –H Æ C = C + H – H | | / \ H H H H

2 a) C2H6 Æ C2H4 + H2

molecular mass 30 28 2mass formed 780 t ? ? = (2/28) x 780 = 56 t

b) Applying conservation of mass 1 000 – 780 – 56 = 164 t164 t of other substances besides the desired product C2H4 andby-product H2 could be produced.

Polymers

Z = H in ethylene.


Investigating LDPE and HDPE1 Branched LDPE polymer chains are kept further apart. The lower

density of LDPE enables it to float on the alcohol-water mixture.

2 The unbranched HDPE chains.

= C and attached Hs

3 Closer packing produces HDPE.

4 LDPE branched molecules cannot get close enough to attractstrongly and so can slip over one another and flex more easily.

5 HDPE unbranched molecules can get closer, attract more stronglythrough dispersion forces and form more compact crystals.

6

HDPE

LDPE

7 LDPE: garbage bags and bins, shampoo bottles, flexible blackirrigation pipes, black agricultural sheets.

HDPE: crinkly shopping bags, freezer bags, milk bottles and crates,buckets, rigid agricultural pipes.

8 HDPE has the greatest crystallinity.


Exercises – Part 1

Exercises 1.1 to 1.3 Name: _________________________________

Exercise 1.1: Petroleum fractions cracked to formethylene

Complete the table below by naming the petroleum fractions – gas, oiland petrol.

Petroleumfraction

Hydro-carbons

Densityg cm–3

BP range°C

Typicaletheneyield %

Typicalpropeneyield %

Typicalmethaneyield %

C3 – C4 – –42 to 0 40 15 25

C5 – C10 0.66 35 to 150 35 14 20

C10–C30 0.82 185 to 335 27 13 12

Use the information in the table to complete the statements about theproducts of cracking.

1 The larger the molecules that are cracked the _____________ the %

yield of ethylene.

2 In the cracking process to form ethylene the by-product

________________ could be used as a fuel while the by-product

_______________ could be used to make polypropylene plastic.


Exercise 1.2: Products from ethylene

Ethylene C2H4 is very reactive and can be used to make a wide range ofcarbon compounds. Complete this table by completing the systematicnames in the second column:

Compound

Common name Systematicname

Structuralformula

Use

ethylene oxide 1,2 epoxyethane (CH2)2O steriliser

acetic acid CH3COOH preserving food

ethylenedichloride

ClCH2CH2Cl fumigant

ethyl chloride chloroethane CH3CH2Cl refrigerant

ethyl bromide CH3CH2Br refrigerant

ethyl alcohol CH3CH2OH disinfectant

Compounds are made from ethylene by a variety of addition reactionssuch as:

• oxidation – addition of oxygen

• halogenation – addition of halogen

• hydrohalogenation – addition of hydrogen halide

• hydration – addition of water.

Use the common names in the table to complete these statements:

__________ and __________ are made by oxidation of ethylene.

__________ is made by halogenation of ethylene.

__________ is made by hydration of ethylene.

_________ and __________are made by hydrohalogenation of ethylene.


Exercise 1.3: Fossil fuel products

The table below shows, by mass, the top 40 chemicals produced in theUSA in 1995.

a) Seven of these 40 chemicals are monomers produced for productionof addition polymers. Name four of the seven using knowledgeacquired in studying Part 1.

b) Tick the 24 chemicals, other than sodium carbonate, urea and carbondioxide, which contain carbon and are fossil fuel products.

c) Put HC in the number column for each chemical that you know is ahydrocarbon.

1 sulfuric acid 43 x 106 tonnes 21 methanol 5.1 x 106 tonnes

2 nitrogen 22 carbon dioxide

3 oxygen 23 xylene C8H10

4 ethylene 24 formaldehyde HCHO

5 lime 25 dimethyl terephthalate C10H10O4

6 ammonia 26 ethylene oxide

7 phosphoric acid 27 hydrochloric acid

8 sodium hydroxide 28 toluene C7H8

9 propylene 29 p-xylene C8H10

10 chlorine 11 x 106 tonnes 30 cumene C9H12 2.6 x 106 tonnes

11 sodium carbonate 31 ammonium sulfate

12 methyl tert-butylether C5H12O 32 ethylene glycol

13 ethylene dichloride 33 acetic acid

14 nitric acid 34 phenol C6H5OH

15 urea (NH2)2CO 35 propylene oxide

16 ammonium nitrate 36 1,3-butadiene

17 benzene C6H6 37 carbon black

18 vinyl chloride 38 isobutylene

19 ethylbenzene C8H11 39 potash

20 styrene 5.2 x 106 tonnes 40 acrylonitrile 1.5 x 106 tonnes



Part 2: Polymers from biomass


AMENDMENTS

Some biopolymers:

PHB-PHV copolymer

C

CH2

CH2

CO

CH

CH3

CH2

C

CH3

O

O O

CCH2

CO

CH3

O

O

C

CH2

CH2

CO

CH3

O

3-hydroxyvalerate3-hydroxypentanoate

3-hydroxybutanoate3-hydroxybutyrate

PLA – polylactide

O C

CH3

H

C

O

polylactide PLA

Cyclodextrin

nonpolardrug

nonpolar drug inpolar cyclodextrin

O

OHHO

HOCH2

HOOH

HOCH2

O

HOCH2

HOOH

+ OO

Part 2: Polymers from biomass 1

Contents

Introduction ............................................................................... 2

Cellulose ................................................................................... 4

Condensation polymers............................................................. 7

Starch and cellulose.............................................................................7

Proteins...............................................................................................10

Polyamides .........................................................................................11

Modelling starch and cellulose molecules.........................................12

Biomass to raw material conversion........................................ 13

Biopolymers ............................................................................ 15

Possible future research directions ...................................................20

Ethanol .................................................................................... 21

Ethanol and ethylene conversion ......................................................21

Ethanol the solvent.............................................................................25

An open ended investigation .............................................................26

IUPAC nomenclature .........................................................................29


Exercises – Part 2 ................................................................... 35


Introduction

The availability of non-renewable resources such as fossils fuels for bothenergy and raw materials varies enormously. The limited supply onEarth have alerted many societies to the importance of reducing theirdependence on fossil fuels. Recently there has been increased support ofscientific research into the use of renewable resources such as biomass.

Biomass is any organic matter produced by photosynthetic conversion oflight energy to chemical energy. Provided the matter involved isrecycled, biomass could be a source of raw materials and energy for aslong as the sun supplies Earth with solar energy.

Scientific research into replacement of non-renewable fossil fuels withrenewable biomass is increasingly supported. There are two mainapproaches:

• biomass to raw material conversion in which chemicals in biomassare converted to molecules which contain carbon chain structuressuch as alkanoic acids, alkanols or hydrocarbons

• production of naturally occurring polymers called biopolymersusing micro-organisms or plants which may or may not begenetically modified.

Ethanol and ethylene are easily interconverted and provide the mostimportant link between biomass based chemicals and petroleum basedchemicals. As you learnt in Part 1, ethylene is the most importantchemical in the production of addition polymers. In Part 2 you will learnabout the other important type of polymers – condensation polymers.


• discuss the need for alternative sources of the compounds presentlyobtained from the petrochemical industry

• explain what is meant by a condensation polymer

• describe the reaction involved when a condensation polymer isformed

• describe the structure of cellulose and identify it as an example of acondensation polymer found as a major component of biomass


• identify that cellulose contains the basic carbon-chain structuresneeded to build petrochemicals and discuss its potential as a rawmaterial

• describe the dehydration of ethanol to ethylene and identify the needfor a catalyst in this process and the catalyst used

• describe the addition of water to ethylene resulting in the productionof ethanol and identify the need for a catalyst in this process and thecatalyst used

• describe and account for the many uses of ethanol as a solvent forpolar and non-polar substances


• use available evidence to gather and present data from secondarysources and analyse progress in the development and use of a namedbiopolymer. This analysis should name the specific enzyme(s) usedor organism used to synthesise the material and an evaluation of theuse or potential use of the polymer produced related to its properties

• process information from secondary sources such as molecularmodel kits, digital technologies or computer simulations to model

– the addition of water to ethylene

– the dehydration of ethanol





energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Cellulose

In this activity you will be investigating cellulose.

What you will need:

• a fresh stick of celery with a leafy top

• access to clean water

• some transparent adhesive tape and a piece of newspaper

• hand lens or magnifying glass

• tincture of iodine solution and a dropper bottle

• a glass or plastic container

• a filter paper.

Method and results:

1 Break off or cut off the top half of the celery stick.

2 Place the top half with a leafy top in a glass or plastic containercontaining a few millilitres of tincture of iodine solution; you mayneed to have the leaves at the top of the celery stick lean againstsomething so the beaker/container does not fall over.

3 Wash the bottom half of the celery stick with clean water and thenstart chewing it. Do all parts of the celery stick taste and chew thesame or do you notice differences?

______________________________________________________

______________________________________________________

Draw the chewed end of the celery stick

In some parts of the world chewed ends of sticks are used astoothbrushes. How clean do your teeth feel now? _____________


4 Take a strip of adhesive tape and place the sticky surface onto apiece of newspaper. Pull the adhesive tape off the newspaper.Can you see cellulose fibres attached to the adhesive tape? A handlens or magnifying glass could be useful here. Draw what you cansee and include information to show the estimated size of the fibres.

5 Tear the edge off a filter paper. Draw what you can see at the tornedge and include information to show the size of any fibres.

6 Place a drop of tincture of iodine on an unprinted part of thenewspaper and on part of the filter paper. Describe what happens.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

7 Place the edge of the newspaper and the edge of the filter paper insome water. Observe what happens, as water moves to, through andbeyond the iodine spots.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

8 Lift the end of the celery stick out of the tincture of iodine solution,wash it with water, then draw what you can see. Once again includeinformation on size in your diagram.


Discussion:

You only need to write the same word five times to complete thediscussion below of your activity.

You have just been investigating:

• the __________ tubes in a stem that carry liquid from roots to leaves

• the __________ rich parts of celery that are hard to eat but do a goodjob of cleaning your teeth

• the fibres of ___________ that make up a newspaper

• the fibres of ___________ that make up a filter paper and trap insoluble residue during filtration

• the fibres of ___________, which although insoluble in water, are able to attract water molecules and draw them upwards by capillary action.

The answer is the name of the chemical that is formed by polymerisationof approximately half of the glucose produced in photosynthesis.5 x 1011 tonnes of the plant material produced on land each year byphotosynthetic fixation of CO2 comprises this chemical – cellulose.

A cellulose molecule Cx(H2O)y contains between 500 and 14 000 glucoseC6H12O6 units and is flat and rigid – ideal as a construction material forthe cell walls of plants and bacteria.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Condensation polymers

The starch in food you eat, cellulose in plant cell walls, proteins found inall living things and nylon plastics are all condensation polymers.

Starch and celluloseCondensation polymers are formed by monomer molecules reactingtogether and eliminating (condensing out) small molecules such as water.

Plants use the glucose produced by photosynthesis to form thecondensation polymers starch and cellulose.

n C6H12O6 Æ (C6H10O5)n + n H2O

monomer Æ polymer + water

O

HO

CH2OH

OH

OH

OH+

O

HO

CH2OH

OH

OH

OH+

O

HO

CH2OH

OH

OH

OH+

O

HO

CH2OH

OH

OH

OH+ etc

section of a starch molecule

O

HO

CH2OH

O

OH

OH

O

CH2OH

O

OH

OH

O

CH2OH

O

OH

OH

O

CH2OH

O

OH

OH

Two hydroxy groups on adjoining glucose molecules react condensingout a water molecule.

O

HO

CH2OH

OH

OH

OH+

O

HO

CH2OH

OH

OH

OH

reactinggroups

O

HO

CH2OH

OH

OH

O

O

CH2OH

OH

OH

OH+ H2O


In the water soluble amylose form of starch the CH2OH groups of theglucose units are on the same side and a spiral structure forms. Every sixglucose units there is one turn of the spiral. A large number of hydroxygroups OH are available on the inside and outside of the spiral to bondwith water molecules and so the starch is water soluble.Spiral arrangement of glucose units in amylose starch

glucose

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

O

OO

O

spiral shape ofamylose starchmolecule

A glucose molecule can exist as an open chain structure or in two closedring structures known as a-glucose (alpha glucose) and b-glucose (beta

glucose). In a glucose solution all three structures are present and thereis rapid conversion between the three structures.

1 CHO

2 CHOH

3 CHOH

4 CHOH

5 CHOH

6 CH2OH

open chain structureglucose ring glucose ring

OH

HO

6 CH2OH

OH

HH

OH

OH

H

OH

HO

6 CH2OH

H

OHH

OH

OH

H

1 14 4

5 5

Number carbons 2 and 3 in the ring diagrams so that you understand theconnection between the three rapidly interchanging structures.

Starch is formed from the a-glucose structure but cellulose forms from

the b-glucose structure.

b-glucose differs from a-glucose in the arrangement of the hydroxy

group around carbon number 1. Compare the positions of the OH groupon carbon 1 in the diagrams above.


For two b-glucose molecules to join, one molecule needs to be upside

down relative to the other molecule.

O

HO

CH2OH

OH

OH

OH+

O

HO

CH2OH

OH

OH

OH

reactinggroups

O

HO

CH2OH

OH

OHO + H2O

OCH2OH

OH

OH

OH

Cellulose is a flat, straight and rigid molecule because the bulky CH2OHgroups are on alternate sides of adjoining glucose units.

O

O

HO

CH2OH

OH

OHO OH

CH2OH

OH

O

O

CH2OH

OH

OHO OH

CH2OH

OH

O

OH

O

HO

CH2OH

OH

OH

OH+

O

OH

CH2OH

OH

OH

HO+

O

HO

CH2OH

OH

OH

OH+

O

OH

CH2OH

OH

OH

HO+ etc

section of a cellulose molecule

Note that the bulky CH2OH groups and the oxygen links betweenglucose units alternate between top and bottom in the diagram.

Many of the hydroxy groups are available to hydrogen bond cellulosemolecules together side by side.

= hydrogen bondingstraight cellulosechains

This forms long strong cellulose fibres that make wood such a strongbuilding material. The reduced availability of hydroxy groups forbonding with water and the joining of cellulose molecules together toform very large aggregations of molecules in fibres makes celluloseinsoluble in water. The high degree of hydrogen bonding between chainsof cellulose also makes it much more resistant to chemical attack.

The hydrogen bonding between the cellulose chains makes the polymerrigid. This reduces the flexing of the chains required in the hydrolysisthat breaks the glucose units apart. Most animals have enzymes thatbreak apart starch in food to obtain glucose. Only a limited number ofanimals (eg termites and cows) contain bacteria with cellulase enzymesable to break apart cellulose to glucose. In the presence of a cellulaseenzyme, water reacts with cellulose forming glucose.


Rigid structure of cellulose

O

O

HO

CH2OH

OH

OHO OH

CH2OH

OH

O

O

CH2OH

OH

OHO OH

CH2OH

OH

O

OH

a) In what ways is the structure of cellulose similar to hydrocarbons frompetroleum?

_____________________________________________________

_____________________________________________________

b) In what ways is the structure of cellulose different fromhydrocarbons?

______________________________________________________

______________________________________________________

c) Which of the hydrocarbons you studied in Part 1 of this module ismost like cellulose?

______________________________________________________

Check your answers.

ProteinsProteins are also condensation polymers:

amino acids Æ protein + water

Each amino acid has an amino group –NH2 and an acid group –COOH.Up to 20 different amino acids can be found in a human protein. Ten ofthe 20 are called essential amino acids because they must be part of ahuman’s diet (eaten as the amino acid or as part of proteins) for propergrowth. The other 10 amino acids can be synthesized by humans fromother chemicals in their diet.


HOOC NH2 + HOOC NH2 + HOOC NH2

HOOC N C

H

O

N C

H

O

N

H

+ water

N C

H

O in proteins is called a peptide linkage (or peptide bond).

PolyamidesSynthetic condensation polymers such as nylon and kevlar also have thesame NHCO linkage. The linkage is called an amide linkage and thepolymers are called polyamidesformation of a polyamide (in this case a nylon)

+ H2N NH2 +Cl ClC

O

C

O

Cl C

O

C

O

C

O

N

H

N

H

C

O

Cl

When this nylon condensation polymer is formed the by-product is notwater. What is the by-product?

_________________________________________________________

Check your answer.

Complete Exercise 2.1: Writing polymerisation equations.


Modelling starch and cellulosemolecules

What you will need:

• metal wire (bare or plastic covered) – at least 1 m length

• means of cutting the metal wire eg. pliers

• plasticine or Blu-tack®.

What you will do:

1 Cut the metal wire in half and then in half again. Wind a quarterlength around a pencil/ballpoint pen then slide the pencil/ballpointpen out. Repeat this procedure to make another spiral. Are thesespirals modelling starch or cellulose? ________________________

2 Cut the remaining metal wire into 10 cm lengths. Place the lengthsside by side then join the lengths together at different points usingplasticine or Blu-tack“. Would this model or the previous model be

best as reinforcing in a structure? ___________________________

3 Design a simple test of the structural strength of these two differentmodels. Describe your test:

4 The colour of iodine depends very much on its surroundings.Concentrated iodine water is brown, dilute iodine water is yellowand iodine in saturated oils such as baby oil is violet. When iodineenters the spiral of a starch molecule interactions between theelectrons of iodine and the starch produce a dark blue colour. Ifcellulose is treated with concentrated sulfuric acid and then iodinesolution a dark blue colour is produced. What structural change doyou think the concentrated sulfuric acid could produce in thecellulose molecules?

______________________________________________________

______________________________________________________

Complete Exercise 2.2: Ironing, cellulose and water.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Biomass to raw material conversion

Biomass is carbon compounds produced by photosynthesis, mostlycellulose. Dried plant material typically consists of 60% cellulose, 20%lignin, 10% protein, 5% sugars and starches and 5% miscellaneouschemicals including fats, oils and waxes.

The challenge in biomass to raw material conversion is to producehydrocarbons or carbon compounds containing hydrocarbon chains suchas alkanoic acids or alkanols from cellulose.

Bacteria and fungi quickly decompose the 15% of dried plant materialmade up of protein, sugars and starches. The lignin and waxes are muchmore resistant to decomposition.

Some bacteria have the ability to decompose the cellulose that is themajor part of biomass. These bacteria secrete cellulases, enzymes orgroups of enzymes which catalyse the reaction of water with highmolecular weight cellulose molecules to produce glucose.

Fermenting anaerobic bacteria can then change the glucose produced tothe C4 to C1 alkanoic acids, carbon dioxide and hydrogen gases.Alkanoic acids with more than two carbons contain C–H bonds as inhydrocarbons. They can be used as feedstock, raw materials for theproduction of chemicals that are usually obtained from fossil fuels.

Molecular formula Systematic name Alternative names

RCOOH alkanoic acid ~~~~~ic acid/alkanoate

HCOOH methanoic acid formic acid/formate

CH3COOH ethanoic acid acetic acid/acetate

CH3CH2COOH propanoic acid propionic acid/propionate

CH3CH2CH2COOH butanoic acid butyric acid/butyrate


Another type of anaerobic bacteria called methanogen bacteria react thecarbon dioxide and hydrogen gases to form methane and water:

4H2 + CO2 Æ CH4 + 2H2O + energy

1 Is this reaction exothermic or endothermic? __________________

2 The energy released by this reaction is used by the methanogen bacteriaas their main energy source. Methane gas is sometimes called marshgas as bubbles of methane are released at the surface of marshes.Where in the marsh do you think the methanogen bacteria are found?

_____________________________________________________

3 Use the information provided above to draw a flow chart showing howthe carbohydrate cellulose can be changed to the hydrocarbon methaneand to alkanoic acids containing hydrocarbon chains.

Check your answer.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Biopolymers

Most plastics are non-degradable polymers made from petrochemicals.Serious environmental problems are posed by the steady increase inplastics production and the resistance of plastics to degradation. Non-degradable plastics are accumulating globally at the rate of over 25million tonnes per year. In 1992 nearly one million tonnes of plasticswere consumed in Australia but only 6% of these were recycled.

Examine your solid waste disposal (garbage). Estimate the % of this volumethat is plastic. _____

How does this compare with United States estimates that one fifth of thevolume of solid waste in landfill sites is plastic? ___________________

Find out the plastics that are recycled in your area. Just because a plasticmaterial has a recycling symbol it does not necessarily mean that there is arecycling program in your area. Even if a plastic material is collected as partof a recycling program this is no guarantee that it will actually be recycled.

1 World production of non-degradable plastics is over 100 million tonnesper year but accumulation in landfill sites and the environment is onlyabout a quarter this rate. How is most plastic waste disposed of so itdoes not accumulate?

_____________________________________________________

2 Explain a disadvantage of the main disposal method.

__________________________________________________________

Check your answer.

It has been estimated that over one million marine animals are killedevery year by either choking on plastics they mistook as food orbecoming entangled in non-degradable plastic debris. In the oceans aLDPE plastic bag can last for nearly twenty years while a HDPE filmcontainer lasts over fifty years. If swallowed by a marine animal thenon-biodegradable plastic is released back into the environment after theanimal dies and the biodegradable polymers of its dead body decay.


A plastic bag in the ocean can act as a serial killer! The global MaritimePollution Treaty (MARPOL) has forbidden the disposal of plastics at seasince 1994. Make sure you dispose of plastic responsibly, especially ifyou live near the coast or waterways.

Signs used by various councils in Sydney read:

‘This leads to Sydney Harbour’ or ‘Part of the Lane Cove River catchment.’

Account for (state reasons for or report on) the use of these signs.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

Many of the problems arising from careless disposal of plastic could beovercome by greater use of biopolymers. Biopolymers are naturallyoccurring polymers generated using renewable resources like micro-organisms or plants. Most importantly biopolymers are biodegradable,that is, decomposed by living things. The biopolymer cellulose in woodis degraded by fungi and some bacteria. Most animals (includingyourself) and most bacteria produce enzymes capable of degrading thebiopolymer starch to the sugar glucose.

Considerable effort is going into replacing non-degradable polymers withbiodegradable biopolymers. eg. the environmental group Greenpeace hasa credit card made from the biopolymer Biopol rather than the commonlyused PVC.

Polyhydroxyalkanoates (PHA) or ‘bacterial plastics’ such as Biopol areextracted from bacteria. Biopol is a mixture of polyhdroxybutyrate(PHB) and polyhydroxyvalerate (PHV) extracted from the bacteriumAlcaligenes eutrophus. Biopol is a thermoplastic, stable in air and humidconditions, and able to degrade in anaerobic conditions such as landfills.

The bacteria are grown in a glucose and valeric acid rich solution. Justas some human beings placed in a food rich environment eat too muchand store energy rich carbon compounds as fat, so the bacteria storeenergy as PHB and PHV. The PHB-PHV copolymer can make up over80% of the mass of dried bacteria. Hot liquid chloroform(trichloromethane) CHCl3 is used to dissolve the copolymer andevaporated off to leave copolymer granules. The copolymer is injectionmoulded into plastic items likely to be left out in the environment such asgolf tees, fishing line and nets and agricultural film sheets.


C

CH2

CH2

CO

CH

CH3

CH2

C

CH3

O

O O

CCH2

CO

CH3

O

O

C

CH2

CH2

CO

CH3

O

3-hydroxyvalerate3-hydroxypentanoate

3-hydroxybutanoate3-hydroxybutyrate

Biopol.

Plates made from PHA-based plastics can be left in place to help healfractured bones; after healing the PHA-based plastic slowly and safelybreaks down in the body. PHB has similar MP, molecular mass,crystallinity and tensile strength to petroleum derived polypropylene PP,the plastic used for climbing ropes and Australian currency notes.

Should all non-biodegradable polymers be replaced with biodegradablepolymers? Because PHB has similar properties to PP should Australiancurrency notes be made from biodegradable PHB instead of non-biodegradable PP?

Polylactic acid or polylactide (PLA) is made from carbohydrates such ascorn starch, waste potato starch and cheese waste.

HO OHC

CH3

H

C

O

lactic acid2-hydroxypropanoic acid

Many units of lactic acid monomer joined together produce polylacticacid/polylactide:

O C

CH3

H

C

O

polylactide PLA

The bacteria used are similar to the bacteria that change lactose sugar inmilk to lactic acid in order to make yoghurt. Fossil fuel is still used togrow and collect the corn, potatoes and milk but the amount of fossil fuelrequired is about half of that needed to produce petrochemical basedpolymers. PLA polymers can be composted and burn like paper orcellulose, producing few by-products and little ash. PLAs have beenused in fabrics for clothing, carpets and outdoor awnings.


Go outside and see if you can find an old spider web. Around lights thatattract insects or outside windows are good places to look. Being careful ofspiders, collect a small amount of material from an old web on your fingers.Test its strength then try to wash it off your fingers with water.

Protein based polymers (PBPs) are what provide the strength of a spiderweb, the elasticity of valves in a 100 year old human heart and theadhesion of an oyster shell on a rock. Research into PBPs concentrateson medical applications, especially as adhesives for wounds and surgerycuts. PBPs can usually be broken down by salt water – PBP plasticsending up in the ocean would not only degrade but at the same time addprotein nutrient to food chains in the marine ecosystem.

Cyclodextrins (CDs) are produced by bacterial action on starch. Theseare small polymers of 6, 7 or 8 glucose units which have an unusualshape.

a-CD b-CD g-CD (gamma CD)

H

H

H

H

C

C

CC

C

O

O

OH

CH2OH

HO

H

H H

H

C

C

CC

C

O

O

OH

CH 2

OH

HO

HH

H

H

CC

C

C

C

O

O

OH

CH

2OH

HO

H

H

H

H

C

C

CC

C

O

O

OH

CH2OH

HOH

HH

H

C

C

CC

C

O

O

OH

CH

2OH

HO

HH

H

H

CC

C

C

C

O

O

OH

CH

2 OH

HO

H

H

H

H

C

C

CC

C

O

O

OH

CH2OH

HO

H

H

H

H

C

C

CC

C

O

O

OHCH 2

OH

HO

H

H

H H

CC

C

CC

O

O

OH

CH

2OH

HO

H

H

H

H

C

C

C C

C

O

O

OH

CH2OH

HO

HH

H

H

CCC

C

C

O

O

OH

CH2OH

HO H

H

H

H

C

C

CC

CO

OOH

CH

2 OH

HO

HH

H

H

CC

C

C

C

O

O

OH

CH2 O

H

HO

H

H

H

H

C

C

CC

C

O

O

OH

CH2OH

HO

HH

H

H

CC

C

C

C

O

O

OHCH 2

OH

HOH

H

H H

C

C

CC

C O

O

OH

CH

2OH

HO

H

H

H

H

C

C

C

C

C

O

O

OH

CH2OH

HO

H

H

H

H

C

C

CC

C

O

O

OH

CH2OH

HO

HH

H

H

CC

C

C

C

O

O

OHCH2OH

HO

HHH

C

C

CC

CO

O

OH

CH

2 OH

HO

H

H

H

H

C

C

C

C

C

O

O

OH

CH2 OH

HO

The insides of these small polymers are rich in C–H and are non-polar.The outsides have many C–OH and are polar.

800

pm

1500 pm

650 pm

600 pm

Approximate dimensions of b-cyclodextrin.


Molecules of low water solubility can dissolve in the hydrophobicinternal cavity. Cyclodextrins can transfer drugs of low water solubility,isolate unpleasant odours or bitter tastes in food and extend the activityof agrochemicals against insect pests and plant diseases.

nonpolardrug

nonpolar drug inpolar cyclodextrin

O

OHHO

HOCH2

HOOH

HOCH2

O

HOCH2

HOOH

+ OO

Cheap biopolymers such as cellulose and starch can be partly changed bychemical reaction to give a more useful product:

1 Rayon (viscose) is chemically treated and regenerated cellulose.

2 Cellulose acetate is used for photographic film and overheadprojector transparencies

3 Methylcellulose is used as a thickener in foods and to increase theviscosity of water and to slow down single celled organismsobserved through a microscope

4 Monostarch phosphate and distarch phosphate are food thickeners.

These chemically modified biopolymers are not as biodegradable as thenatural biopolymers that they are made from.

Complete Exercise 2.3. Using the Internet for information on progress indevelopment and use of a biopolymer

To learn more about applications of biopolymers go towww.lmpc.edu.au/science


Possible future research directionsAt present the production price of biopolymers is five to fifteen times theprice of petrochemical polymers. As uses for biopolymers increase andlarger industrial works are built that are comparable in capacity toindustrial works for petrochemical polymers, their production priceshould decrease.

However to obtain the million ton scale of product needed to reduceprice, large natural producers such as crop plants rather than smallbacteria will need to be used.

Biopolymers cost about US$5-15/kg compared with about US$1/kg forsynthetic plastics from petroleum. If biopolymers could be produced bycrop plants the way food oils (US$0.50/kg) and corn starch (US$0.25/kg)are, then prices could be well below that of petroleum based plastics.

To do this genetic engineering (= genetic modification = geneticmanipulation) will be required to transfer suitable genetic material intoplants. Spider web silk genes have already been transferred to thecommon bacterium E. coli and produced protein-based polymers (PBPs).These genes could be transferred to a crop plant and express themselves,that is produce protein polymer, in leaves or other parts of the crop plantnot used for food. Harvesting PBPs from leaves would be much cheaperthan carrying out the expensive process of fermentation using E. Colibacteria.

Complete Exercise 2.4: Biopolymers currently in use.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Ethanol

Ethanol and ethylene conversionAny country which has a source of ethanol or ethylene can establish achemical industry capable of producing a wide range of chemicals.

Countries such as Brazil, with climate and land suitable for growingextensive crops, can base the chemical industry on producing ethanolfrom plant material. Countries around the Persian Gulf where two-thirdsof the world’s known petroleum reserves are located or countries withmajor petroleum refineries such as Singapore can base the industry onethylene.

Sulfuric acid, phosphoric acid and heated ceramic solids can be used tocatalyse conversions between ethanol and ethylene.

To understand why conversion between ethanol and ethylene involvinghydration or dehydration is so easy, carry out the activity below.

In this activity you will be representing a chemical change using a molecularmodel kit.

What you will need:

• A molecular model kit or maltesers and toothpicks and a red markerpen or coloured jelly jubes/marshmallows and toothpicks.

Use different coloured atoms for C (usually black), O (usually white) andH (usually red) if using a molecular model kit.

Or, use maltesers for C, maltesers with most of the chocolate removed torepresent O and red marks on the end of a toothpick to represent H.

Or, use different coloured jelly jubes/marshmallows to represent C, Oand H. C and O should be about the same size but make the H smaller.


What you will do:

Make a 3-dimensional model each of ethanol, ethylene and water.

The 2-dimensional drawings below showing angles of 90° and 180°(for ease of printing) are not the angles in actual 3-dimensional models.

The approximate angles you should use between bonds in your3-dimensional models are shown below the 2-dimensional formulas.

H H H H | | dehydration | | H – C – C – O – H C = C + H – O – H | | hydration | | H H H H

109° 120° 105°

In Part 3 of the Energy module pages 5 and 6, diagrams of the type below were used totry to show the 3-dimensional nature of molecules. These diagrams show the first threemembers of the alkane series:

C

H

H HH

methane CH4

C

H

HH C

H

H

H

ethane C2H6

C

H

H

H

HH

CC

H

HH

propane C3H8


1 Using the type of diagrams shown on the previous page, drawdiagrams to show the 3-dimensional nature of the molecules in thedehydration/hydration equation.

2 In Part 4 of the Preliminary Energy module (see pages 11-14) youcalculated the energy change for a chemical reaction from bondenergy values.

Use the methods from the Energy module to calculate the energychange for the reaction: Compare the total amount of energyabsorbed in breaking bonds (positive values) with the total amountof energy released when bonds are formed (negative values).Bond energy values needed for calculations are given below in kJmol–1:C–C 346, C–H 414, O–H 463, C–O 358, C=C 614.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

3 State the DH for the dehydration of ethanol.

_____________________________________________________

4 State the DH for the hydration of ethylene:

_____________________________________________________

5 Which of these two processes is endothermic?

_____________________________________________________


6 Explain why the reverse process, the exothermic process, does notoccur spontaneously. Why does an exothermic process need energyfor the reaction to start?

______________________________________________________

______________________________________________________

______________________________________________________

7 Both the dehydration of ethanol and hydration of ethylene reactionsrequire the presence of a catalyst. Heated clay or porous ceramicmaterial can act as catalysts. These solid catalysts have polar sitesthat attract the electron rich C=C and polar OH groups of water.The close proximity of the molecules and heat, which providesactivation energy, speed up the reaction. Explain why a catalystspeeds up both the forward and the reverse reaction.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

8 In industry solid catalysts such as aluminium oxide and conditions of70 atmosphere pressure and 300°C are used. Explain how highpressure and high temperature can increase rate of a reaction.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.


Ethanol the solventAfter water, ethanol is probably the most important solvent for industrialapplications and consumer products. Ethanol is the least toxic to humansof all the alcohols so most consumer products that list alcohol containethyl alcohol (ethanol).

Most alcohols are volatile, flammable liquids. The most toxic is methylalcohol (methanol) CH3OH. Alcohols are less damaging to the skin thanmost other solvents.

Complete Exercise 2.5: Chemical labels. This requires you to survey thechemical labels in your home and list all products containing alcohol (orethanol). You will also be asked to record the names of any compoundending in -ol (eg. cholesterol, glycerol) as these are practically alwaysalcohols.

Did you find most of the alcohols listed in products were ethanol?Suggest two reasons why ethanol is the most common alcohol used.

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

The use of pure ethanol is strictly controlled by governments. This isbecause ethanol is the alcohol in alcoholic drinks. A person drinking100 mL or more of alcohol per day often has, or is developing, a healthproblem. Smaller amounts of daily alcohol consumption can causedamage to an unborn child. To control consumption of alcohol and toraise revenue, governments impose a special tax called excise on the saleof alcoholic drinks. There are also special controls on the amount ofalcoholic drinks a person can brew (beer), ferment (wine) or distill toincrease the alcohol concentration (spirits).

Methylated spirits or denatured alcohol is 90-95% ethanol, 0-5%methanol, 5% water and small amounts of chemicals to make the liquiddistasteful. The denatured form of ethanol is useful as a solvent andcleaning aid and is sold cheaply without excise. The chemicals added areto try to stop alcoholics from drinking methylated spirits for the ethanolcontent. The most bitter compound known, trade name Bitrex®, issometimes added. As little as 30 ppm of Bitrex® makes the liquid toobitter to be tolerated by most humans.


An open ended investigationIn this open ended investigation you are required to plan, chooseequipment and perform a first-hand investigation to gather informationabout the range of household substances that can be dissolved by ethanol.

For practical work, instead of ethanol (very difficult to obtain in pureform) you are asked to use methylated spirits.

Methylated spirits is highly inflammable and toxic if ingested (drunk oreaten). Avoid inhalation – use it in a well ventilated area. Skin irritant onprolonged contact.

Waste solutions may be disposed of down a sink hole to the sewer. Mostimportantly, keep methylated spirits away from sources of heat, flame andspark.

This open ended investigation has two parts, A and B.

Part A:

Use information resources to find the solubility of pure chemicals inethanol.

Here is a list of resources you could try:

• books at home

• books at a public, school or TAFE library

• websites on the worldwide web. A search engine could be useful infinding appropriate sites; if you have difficulties try a search enginesearch using MSDS for material safety data sheets.

MSDSs are information sheets which chemical suppliers must makeavailable when they supply chemicals. At the beginning of a MSDS,just above the list of physical properties, there is often informationabout solubility in alcohol (ethanol).

• your teacher may allow you to have access to the CD ROM with theChemical Safety in Schools package supplied to NSW schools inJuly 2000.

This CD ROM contains the CHEMWATCH chemical database andmanagement system with over 20 000 material safety data sheets.Although the CD ROM is marked for use with IBM compatible andMacintosh systems the MSDSs part can only be accessed using anIBM compatible computer.


Part B

Use chemicals you have at home and test their solubility in methylatedspirits.

You will need to design a procedure that is:

• fair

• valid (leading to effective results and worthwhile conclusions) and

• reliable (trustworthy, giving similar results if repeated).

Here are some tips before you begin:

1 If possible use test tubes—they are easy to see through and can beeffectively shaken

2 You may need a wooden skewer to push solid to the bottom of thetest tube before adding the solvent

3 When testing solubility of a liquid in a solvent add more solvent thanliquid solute. If the two liquids are immiscible (do not mix) it willbe easier to tell which is the solvent (as it will have the largestvolume).

4 Instead of mixing the substance directly with methylated spirits youcould take an inert fabric eg. cotton sheet, and mark it in sectionswith a variety of liquids and solids.

Cut the sheet into squares of the same size and then add the separatesquares to methylated spirits in different test tubes.

Shake all the samples in the same way, remove the sheet and dry inair to see which of the marks has dissolved.

Once you have mentally worked out what procedure you will use in Part Aand Part B, turn to exercise 2.6. Draft your plan.

Do NOT perform the investigation until after your plan has been returned toyou with comments from your teacher.

Your full report of the investigation is Exercise 6.1 in Part 6 at the end ofthis module.

Exercise 6.2 in Part 6 is based upon your experiences in carrying out thisopen ended investigation.


Solvent properties and molecular structure

Some physical properties of straight chain alkanols

Structural formula Molecularmass

MP(°C)

Water solubility(g/100 g water)

CH3OH 32 –98 infinite

CH3CH2OH 46 –114 infinite

CH3CH2CH2OH 60 –126 infinite

CH3CH2CH2CH2OH 74 –90 7.9

CH3CH2CH2CH2CH2OH 88 –79 2.3

CH3CH2CH2CH2CH2CH2OH 102 –45 0.6

CH3CH2CH2CH2CH2CH2CH2OH 116 –34 0.2

CH3CH2CH2CH2CH2CH2CH2CH2OH 130 –15 0.05

Each of these alkanols consists of:

• a hydrophilic (water loving) OH group that can hydrogen bond withwater and, because it is polar, attract ions and polar molecules

• a hydrophobic (water fearing) or lyophilic (fat loving) non-polarhydrocarbon chain that can attract non-polar molecules.

The first three members of the homologous series, methanol, ethanol and1-propanol mix with water in all proportions.

Going further down the homologous series the water solubility of thealkanols decreases as the hydrocarbon chain becomes a large part of eachmolecule.

Explain why ethanol can dissolve a wide range of substances such as salts,polar molecules and non-polar molecules.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.


IUPAC nomenclatureIUPAC is the International Union of Pure and Applied Chemistry. Thisinternational organisation encourages systematic naming of chemicals.IUPAC is the organisation that the chemists of the world turn to, for helpand guidance in naming (nomenclature) of chemicals.

Use your experience with naming the alkane hydrocarbons in thePreliminary course to complete the systematic names for alkanols. The 1-prefix indicates that the –OH group is attached to an end carbon atom.

Structural formula Systematicname

Trivial name

CH3OH methanol methyl alcohol

CH3CH2OH ethanol ethyl alcohol

CH3CH2CH2OH 1-propanol n-propyl alcohol

CH3CH2CH2CH2OH n-butyl alcohol

CH3CH2CH2CH2CH2OH n-pentyl alcohol

CH3CH2CH2CH2CH2CH2OH n-hexyl alcohol

CH3CH2CH2CH2CH2CH2CH2OH n-heptyl alcohol

CH3CH2CH2CH2CH2CH2CH2CH2OH n-octyl alcohol

Check your answers.

A different number is used if the hydroxy group is attached to a carbonwhich is not on the end of the chain. The number shows the carbon towhich the OH group is attached, counting from the end that gives thelowest number.

e.g CH CH CH CHOHCH3 2 2 3 is 2-pentanol as OH is on carbon secondfrom the right hand side CH CHOHCH CH CH3 2 2 3 is also 2-pentanol as OH is also on carbonsecond from the left hand side CH CH CHOHCH CH3 2 2 3 is 3-pentanol as OH is on carbon 3 countingfrom the left or the right.


Suggested answers

Condensation polymersa) Cellulose is similar to hydrocarbons because it contains C–C bonds

and C–H bonds.

b) Cellulose contains C–O–H and C–O–C bonds which are not inhydrocarbons. Cellulose molecules are attracted to one another byhydrogen bonds between OH groups. Hydrogen bonding betweencellulose molecules is much stronger than the dispersion forces thatoccur between hydrocarbon molecules.

c) High density polyethene HDPE is most like cellulose because it alsoconsists of linear molecules.

The by-product in the formation of nylon is hydrogen chloride HCl.

Modelling starch and cellulose molecules1 Starch is a spiral shaped molecule.

2 Straight lengths joined at points should distort less than spirals.

3 Test should apply same force in same conditions and compareamount of distortion of the two different models.

4 The sulfuric acid appears to have changed the linear structure ofcellulose to produce the spirals which can interact with iodineproducing a dark blue colour.

Biomass to raw material conversion1 Exothermic as energy is released.

2 Methanogen bacteria would be found near the anaerobic bacteria thatproduce the raw materials they need – carbon dioxide and hydrogen.Thus methanogen bacteria would probably at the bottom of themarsh well away from air.


3 Flow chart showing how cellulose can be changed to methane andalkanoic acids

cellulose(C6H10O5)n

waterH2O

cellulase

glucoseC6H12O6

butanoic acidC3H7COOH

propanoic acidC2H5COOH

ethanoic acidCH3COOH

methanoic acidHCOOH

carbondioxideCO2

hydrogenH2

methanogen bacteria

methaneCH4

waterH2O

anaerobic bacteria

Biopolymers1 Most plastic waste is spread around the environment or burnt instead

of disposal in landfill. Some is recycled.

2 Spreading around the environment creates visual pollution andthreatens wildlife. Burning of plastics can release harmfulsubstances into the environment such as hydrogen halide gases anddioxins.

Signs such as ‘This leads to Sydney Harbour’ or ‘Part of the Lane CoveRiver catchment’ are to make people conscious that rubbish left ingutters will be carried by water to the harbour or rivers.

Ethanol and ethene conversion1

O

H

HH

C

H

H

H

C

H

H H

C

C

H H

OH

+


2 H H H H | | dehydration | | H – C – C – O – H C = C + H – O – H | | hydration | | H H H H

Bonds broken Bonds formed

5 x C–H 4 x C–H

1 x C–C 1 x C=C

1 x C–O 2 x O–H

1 x O–H

Energy in Energy out

(5x414)+346+358+463 (4x414)+614+(2x463)

= 3237 3196

DH = 3237 – 3196 = 41 kJ

3 DH = 41 kJ per mole of ethanol

4 DH = – 41 kJ per mole of ethylene

5 The dehydration of ethanol is endothermic.

6 Energy is released during reaction but to start reacting the ethyleneand water need sufficient energy to exceed the activation energy.

7 A catalyst provides an alternative pathway with a lower activationenergy. The pathway is the same but direction different for forwardand reverse reactions.

8 High pressure increases the chances of collision. High temperatureslightly increases the chances of collision while significantlyincreasing the likelihood that the colliding molecules will exceed theactivation energy and react.

Ethanol the solvent

Ethanol is the least toxic alcohol, cheap and water soluble.


Solvent properties and molecular structure

Ethanol has both a polar OH group that attracts salt ions and polarmolecules and a non-polar hydrocarbon chain that attracts non-polarmolecules.

IUPAC nomenclature

Structural formula Systematicname

Trivial name

CH3OH methanol methyl alcohol

CH3CH2OH ethanol ethyl alcohol

CH3CH2CH2OH 1-propanol n-propyl alcohol

CH3CH2CH2CH2OH 1-butanol n-butyl alcohol

CH3CH2CH2CH2CH2OH 1-pentanol n-pentyl alcohol

CH3CH2CH2CH2CH2CH2OH 1-hexanol n-hexyl alcohol

CH3CH2CH2CH2CH2CH2CH2OH 1-heptanol n-heptyl alcohol

CH3CH2CH2CH2CH2CH2CH2CH2OH 1-octanol n-octyl alcohol




Exercise 2.1: Writing polymerisation equations

Write equations to represent the formation of :

a) an addition polymer from petrochemicals [Hint: see Part 1]

b) a condensation polymer from petrochemicals

c) a condensation polymer from biologically produced chemicals


Exercise 2.2: Ironing, cellulose and water

Important fabrics such as cotton, calico and linen are composed ofcellulose fibres. Fabrics crease. To remove the creases these fabricsneed to be either sprayed with cold water and then hot ironed or,alternatively, ironed with a steam iron that sprays the fabric with hotwater and steam then heats the fabric. The water added to cellulosefabrics acts as a plasticiser.

a) Use your knowledge of chemistry to predict what happens to:

i) cellulose molecules when they are sprayed with water or steam

__________________________________________________

__________________________________________________

__________________________________________________

ii) cellulose molecules when they have the water removed fromthem by heating

__________________________________________________

__________________________________________________

__________________________________________________

iii) dry cotton that is creased then hot ironed compared with whathappens to wet cotton that is creased then hot ironed.

__________________________________________________

__________________________________________________

__________________________________________________

b) Which one of the three predictions could you best test with anexperiment?

______________________________________________________

c) Carry out an appropriate experiment and report your results:

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

d) Look at the temperature scale on a steam iron. How resistant arecellulose fabrics to heat compared with synthetic fabrics?

______________________________________________________

______________________________________________________


Exercise 2.3: Using the Internet for information onprogress in development and use of a biopolymer

Use a search engine such as www.google.com to gather information onone of the newly developed biopolymers.

a) Name of biopolymer chosen:______________________________

b) Name of enzyme or organism used to synthesise the biopolymer:

_____________________________________________________

c) Progress in development of the biopolymer:

_____________________________________________________

_____________________________________________________

_____________________________________________________

d) Use(s) of the biopolymer:

_____________________________________________________

_____________________________________________________

_____________________________________________________

e) Properties of the biopolymer relevant to use or potential use:

_____________________________________________________

_____________________________________________________

_____________________________________________________

f) Your evaluation of the use or potential use of the polymer related toits properties:

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________


Exercise 2.4: Biopolymers currently in use

Biopolymer Use Foodprocessing

Pharmaceuticals Cosmetics

xanthan thickener � �

alginate dispersant � �

gelatin stabiliser �

carrageenan humectant �

hyaluronicacid

lubricant �

a) Use the information to find a product in your home that contains oneof these biopolymers.

i) Name of biopolymer

__________________________________________________

ii) Name of product

__________________________________________________

iii) Dictionary definition of its use

__________________________________________________

__________________________________________________

__________________________________________________

b) Look at the other components of the product. Predict why thisbiopolymer has been added to the product.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________


Exercise 2.5: Chemical labels

Survey chemical labels in your home. List products containing alcohol,ethanol or an –ol name.

Product Names of alcohols


Exercise 2.6: Draft plan for an open endedinvestigation

Part A:

Part B:

Gill Sans Bold



Part 3: Renewable ethanol


AMENDMENTS

ethanol glucose

sucrose

starch

cellulose

CO2

H2O

food

for organisms

fuel for

burning

photosynthesis

energy released energy absorbed

Ethanol – a renewable fuel

Corn starch amylase glucose yeast ethanol

Cane sugar waste yeast ethanol

Wheat starch waste glucose ethanol

Biomasscellulase or sulfuric

acid solution glucosegenetically

engineered yeast bioethanol

amylase yeast

Part 3: Renewable ethanol 1

Contents

Introduction ............................................................................... 2

Ethanol: a renewable source of energy ..................................... 4

Biomass to energy conversion .................................................. 7

Converting plant material to ethanol....................................................9

Fermentation ........................................................................... 11

Mass changes in fermentation...........................................................13

Molar heat of combustion ........................................................ 16

Measuring molar heat of combustion of liquid alkanols....................19

Comparing practical and theoretical values......................................22

Appendix: Fermentation to make ginger beer ......................... 25


Exercises – Part 3 ................................................................... 31


Introduction

Ethanol is the main fuel produced from plant material, a renewableresource. As fossil fuels which are non-renewable resources aredepleted, ethanol and other products from renewable resources will be ofincreasing importance.

Part 3 concentrates on how ethanol from renewable plant material isincreasingly important as a source of energy replacing fossil fuels.


• outline the use of ethanol as a fuel and explain why it can be called arenewable resource

• describe conditions under which fermentation of sugars is promoted

• summarise the chemistry of the fermentation process

• define the molar heat of combustion of a compound and calculate thevalue for ethanol from first-hand data

• assess the potential of ethanol as an alternative fuel and discuss theadvantages and disadvantages of its use

• identify the IUPAC nomenclature for straight-chained alkanols fromC1 to C8.


• process information from secondary sources to summarise theprocesses involved in the industrial production of ethanol from sugarcane

• process information from secondary sources to summarise the use ofethanol as an alternative car fuel, evaluating the success of currentusage

• solve problems, plan and perform a first-hand investigation to carryout the fermentation of glucose and monitor mass changes

• present information from secondary sources by writing a balancedequation for the fermentation of glucose to ethanol


• identify data sources, choose resources and perform a first-handinvestigation to determine and compare heats of combustion of atleast three liquid alkanols per gram and per mole.





energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Ethanol: a renewable source of energy

In 1908, when Henry Ford was designing his Model T Ford, the firstmass produced car, he designed the engine to run on alcohol. Howeverplentiful supplies of petroleum removed the incentives to produceethanol for internal combustion engines. Fossil-fueled petrol, dieseland LPG engines became the norm for the twentieth century.

If an engine uses 10-20% anhydrous ethanol in petrol the engine can usethe same carburettor or fuel injection system as for 100% petrol. Anengine designed to run on distilled alcohol which is 96% ethanol and 4%water requires a different carburettor. Both type of engines produce lesspollutants than a 100% petrol engine.

If the ethanol is produced from cellulose biomass rather than starch orsugar, it is often called bioethanol. Ethanol made from plant materials isa renewable source of energy.

A full fuel-cycle study carried out by the US Department of Energy at theend of 1997 included the energy required to grow and harvest corn, distillethanol from starch fermentation mixtures and transport it to petrolstations.

This study showed a reduction in fossil energy use of 50-60% andgreenhouse gas emissions of 35-46% compared with conventional petrol.Reduction in greenhouse emissions and fossil energy use were calculatedto be even greater if bioethanol was produced from the cellulose of cornplants.

1 Write a balanced equation for the complete combustion of ethanol.

_____________________________________________________

2 Name the two main products of the complete combustion of ethanol.

_____________________________________________________

3 What types of energy are released in the combustion of ethanol?

_____________________________________________________

4 Write a balanced equation for photosynthesis.

_____________________________________________________


5 Name the two reactants required for photosynthesis.

_____________________________________________________

6 What type of energy is absorbed in photosynthesis?

_____________________________________________________

7 Draw a labelled cycle diagram to explain why ethanol can be calleda renewable resource.

Check your answers.

Ethanol as a car fuel

In this activity you will be evaluating current usage of ethanol as analternative car fuel. Evaluating means ‘determining the value of’.

Evaluating current usage requires you to obtain up-to-date information.Check the date of publication of any source that you use.

1 Which should be the more reliable source of information? A book firstpublished in 1992 and reprinted in 1998 or a second book first publishedin 1992 and revised in 1996?

_____________________________________________________

_____________________________________________________

2 Do not assume all websites are equal. A website may have been lastrevised in 1996 while another may have been revised in 1999.Which should give information closest to current usage?

_____________________________________________________


3 Consider the type of web site you are accessing:

.com indicates a business

.org indicates a non-profit organization

.edu indicates an educational establishment

.au indicates an Australian web site

.br indicates a Brazilian web site – this could be in Portuguese

No country symbol indicates a USA site

Which type of site do you think would give the most reliableinformation?Justify (support) your answer.

______________________________________________________

______________________________________________________

______________________________________________________

4 After researching information using books, magazines, newspapersand the Internet summarise your information. Which source wasmost useful?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

5 Evaluate the success of current usage of ethanol as an alternative carfuel.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.

This information is needed to complete Exercise 3.1



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Biomass to energy conversion

The amount of energy captured by biosynthetic conversion of lightenergy to chemical energy is probably ‘an order of magnitude’ greaterthan the amount of energy used by the world’s human population.

[Do you remember that order of magnitude refers to powers of 10? 102 isone order of magnitude greater than 101 while 104 is three orders ofmagnitude greater than 101. ‘an order of magnitude’ greater means about10 times larger.]

In other words solar energy is stored in plants at about 10 times the ratethat energy is required for the activities of over six billion human beings.Only about 5% of a typical crop plant is harvested as food. If the energystored in the remaining, largely unused, 95% of crop plants could beconverted to energy this would reduce human dependence on fossil fuelenergy resources significantly.

The energy stored in carbon compounds in biomass could be released by:

• burning dry plants or plant products instead of fossil fuels in electricpower stations eg. waste wood from forestry, straw and grain husksfrom cereal grains, crushed cane after cane sugar extraction

• converting cellulose to methane using anaerobic bacteria eg. animalwaste from intensive animal farming of pigs and chickens, cattledung from meat or dairy production; the methane can be burnt as animpure gaseous fuel

• converting starches and sugars in cereal or sugar cane waste toethanol by fermentation; the ethanol needs to be separated from anethanol rich water fermentation mix before use in internalcombustion engines.

All of these methods have been tried in Australia but many of them areconsidered uneconomic when fossil fuels are so readily available andcheap. The gathering of dry plants or plant products requires input offossil fuel to operate machinery and transport, waste cellulose digestersrequire construction of collection channels from intensive animal farmsand considerable energy is required to separate ethanol fromfermentation mixtures by distillation.


As non-renewable fossil fuels become more difficult to obtain and moreexpensive, greater use may be made of renewable biomass as an energysource.

Countries trying to reduce dependence on imports of fossil fuels, such asthe United States and Brazil, are often prepared to support biomass toenergy conversion. In the USA (3% of the world’s oil reserves whileconsuming 25% of the world’s oil) government subsidises the price ofethanol. Brazil with hardly any oil reserves has reduced its dependenceon large imports of petroleum by using its vast land resources and sugarcane production to produce ethanol.

Here are some examples of current research directions in biomass toenergy conversion:

• The biomass is a porous solid material so research is focussed onways of improving movement of water and acid from solution intothe solid and movement of sugars out of solid into the solution.

• Major advances have been made by genetic modification of abacterium called Zymomonas mobilis. This bacterium has a shorterfermentation time (three or four times faster than yeast) andproduces more ethanol per kg of plant material than yeastferrmentation.

• Distillation of ethanol from the fermentation mixture can require halfthe energy released when the ethanol is used as a fuel. Distillation isbeing replaced by low energy methods such as using solid zeoliteminerals as filters to separate ethanol from fermentation mixtures.

= HOH

= CH3CH2OH

zeolite filter trapped water

pure ethanol

The trapped water molecules are strongly attracted to polar parts of thezeolite.


Converting plant material to ethanol

There are a number of methods of converting plant materials to ethanol:

Corn starch amylase glucose yeast ethanol

Cane sugar waste yeast ethanol

Wheat starch waste glucose ethanol

Biomasscellulase or sulfuric

acid solution glucosegenetically

engineered yeast bioethanol

amylase yeast

Bioethanol is ethanol produced from cellulose in biomass, rather thanstarch or sugar in biomass. Bioethanol is the same chemical asethanol, C2H5OH. Bioethanol is simply ethanol that has been obtained,with greater difficulty, from the more plentiful resource cellulose.

The ethanol produced is a valuable raw material for producing otherchemicals. For example dehydration of ethanol C2H5OH Æ C2H4 + H2Oproduces ethylene. Ethylene can be polymerised or used to make otherpolymer monomers. Thus renewable biomass can be converted to thehydrocarbon ethylene which normally comes from non-renewablepetroleum.

Use this information to complete the following sentences:

1 Amylase is an enzyme which hydrolyses the polymer starch to form themonomer ____________.

2 Cellulase is an enzyme which hydrolyses the polymer ___________to form sugar monomers.

3 The names of _________ usually end in the letters ‘ase’

4 The names of carbohydrates such as glucose, sucrose, amylose andcellulose usually end in the letters ‘___’.

5 Enzymes from yeast are used to convert glucose to ________.

6 The method which is used for waste wood uses the enzyme____________ or _____________ acid.


7 One of these four methods shown in the diagram is based on recentdevelopments in technology. Name the method which is a recentdevelopment and justify your answer.

______________________________________________________

______________________________________________________

______________________________________________________

8 Use a search engine such as http://www.google.com to find out whichof the above processes is carried out by the following:

a) The Manildra Group at Nowra, NSW, Australia.

__________________________________________________

__________________________________________________

__________________________________________________

b) CSR at Sarina, Queensland, Australia.

__________________________________________________

__________________________________________________

__________________________________________________

9 Disposal of solid waste (garbage) is a major problem for citiesthroughout the world. One of the four methods (shown in theprevious diagram for converting plant material to ethanol) has beensuggested as being appropriate for solid waste disposal sites nearcities. The ethanol produced could be used as a fuel for city motorvehicles as ethanol is 35% oxygen by mass. This oxygen enhancesthe burning of petrol resulting in more efficient burning and reducedexhaust emissions.

• Predict which of the four methods is a possible future directionof chemical research on solid waste disposal by cities

__________________________________________________

• Justify your prediction.

__________________________________________________

__________________________________________________

• Identify the two most suitable starting materials for this processpresent in solid waste that is a mixture of plastic, paper, metal,glass and food scraps.

__________________________________________________

Check your answers.


Fermentation

Fermentation is controlled chemical change catalysed by enzymes fromorganisms such as yeast or bacteria. Fermentation producing ethanol iseasily carried out using any plant material containing sugar and yeast.

Next time you come across an old bunch of grapes have a close look atthe surface of the grapes. You’ll probably be able to see a dull fuzzylayer on parts of some grapes. These are yeast moulds waiting for anopportunity to penetrate the grape skin and get in to have a feed on thesugars within! The chemical action of yeasts on grape juice produce thealcohol and chemical flavours of wines. Different yeasts can producedifferent chemical flavours.

Sour grapes in a bunch of sweet grapes are the ones that have had theirsurface penetrated by yeast and have started to ferment. The sourness isdue to an acid intermediate produced as sugar changes to ethanol.

The yeast organisms can act on a variety of sugars. For example canesugar, sucrose, C12H22O11 is hydrolysed to form glucose C6H12O6 andfructose C6H12O6.

C12H22O11 + H2O Æ C6H12O6 + C6H12O6

sucrose + water Æ glucose + fructose

Glucose and fructose are isomers (same molecular, different structuralformulas). Both glucose and fructose can be changed to ethanol andcarbon dioxide. The pathways used by organisms to change chemicalsare called metabolic pathways.

A lot of genetic engineering research involves introducing genes for ametabolic pathway from one organism into another organism. This isknown as metabolic engineering. Each step in a metabolic pathwayusually requires a specific enzyme. Each specific enzyme is produced bya specific gene or genes. Studying metabolic pathways is an importantpart of the option The biochemistry of movement of the Stage 6Chemistry syllabus.


Fermentation of plant material rich in starch uses organisms that containenzymes able to change starch to sugars: starch + water Æ sugars

(C6H10O5)n + nH2O Æ n C6H12O6

The sugars are then fermented to alcohols.

C6H12O6(aq) Æ 2C2H5OH(aq) + 2CO2(g)

After fermentation the mixture can be distilled to make spirits eg. whiskyfrom fermented barley or corn, vodka from fermented potatoes.The different flavours of alcoholic drinks come from hundreds ofby-products. Reactions involving organic compounds rarely give 100%conversion to the anticipated products. By-products are typical oforganic reactions. Different types of grapes and fermentation conditionsresult in different by-products and a huge variety of wines.

1 When pure glucose C6H12O6 undergoes fermentation only two productsare formed – ethanol C2H5OH and carbon dioxide CO2.

glucose Æ ethanol + carbon dioxide

Write a balanced equation for this fermentation reaction.

______________________________________________________

2 Fermentation can only be carried out in solution. Name theimportant solvent required for all fermentation reactions.

______________________________________________________

3 Each separate step in changing sugars to ethanol and carbon dioxideis catalysed. The catalysts work best at a temperature of 20 to 30°C.What type of catalysts are these and where do they come from?

______________________________________________________

______________________________________________________

4 Unfortunately for the yeast organisms they die of alcoholicpoisoning once the concentration of ethanol reaches about 15% v/v!Most wines are up to about 12% ethanol by volume. How arealcoholic drinks with much higher concentrations, such as brandy,obtained from wine?

______________________________________________________

______________________________________________________

Check your answers.


Mass changes in fermentation

What you will need:

• a balance capable of weighing to at least the nearest gram

• a gas tight container (in which to carry out the fermentation) with a tubepassing to a smaller container

• 25 g of glucose C6H12O6 or sucrose (table sugar) C12H22O11

• 1 g of table salt

• 7 g dried yeast (found in the bread making or flour section of asupermarket – usually in 7g, 12g or 28 g packets)

• 250 mL of water

• a warm area to place the equipment (20-30°C is suitable)

• limewater Ca(OH)2(aq) to half fill the smaller container.

Keep lime and limewater away from eyes and skin. Lime or limewater ineyes must be immediately washed away with lots of water.

Limewater is made by adding a small amount of lime (a chemicalobtainable from a hardware store, bricklayer or builder) to asealable container half filled with water. (Do not use lime from anursery or agricultural supplier—this is usually powderedlimestone, calcium carbonate CaCO3).

Shake the lime with the water then add more water until thecontainer is almost full. Some of the solid lime, Ca(OH)2(s), willdissolve to form a water solution, Ca(OH)2(aq). Prepare thelimewater at least one day before you start the activity becauseCa(OH)2(s) is not very soluble in water and takes a while to formCa(OH)2(aq).

Seal the container and always keep it topped up with water tominimise contact with air. When the limewater is needed it isdecanted as a colourless, transparent solution and the containerresealed.

Limewater turns cloudy when exposed to CO2 becauseCa(OH)2(aq) + CO2(g) Æ CaCO3(s) + H2O(l).The small particles of CaCO3(s) formed reflect light like clouds do.


Laboratory equipment

cut hole forstraw inplastic bottle

push strawthrough the lid

bend straw to fitin small plasticcontainer

ensure straw isimmersed in water

fill 1§3 full with water

place powdered yeast into sugar solution

dissolve sugar

stir in acircularmotion

seal straw

Home equipment

Method

1 Place the fermentation mixture of sugar, water, salt and yeast intothe larger container and swirl to mix. Weigh the container andcontents and attached equipment for transferring gas.

2 Half fill the smaller container with limewater. Weigh the containerof limewater.

3 Put the two containers in a warm area.

4 Place the end of the gas transferring equipment so that any gasproduced in the large container enters the limewater about 1 cmbelow the limewater surface.

5 Record the appearance of the fermentation mixture and limewater inthe results table.

6 Repeat the weighings and observations daily at least every secondday for a week.


Results

Fermentation mixture LimewaterDate

mass (g) appearance mass (g) appearance

Conclusions

1 Is there any connection between change in mass of the fermentationmixture and change in mass of the limewater?

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Explain the change in mass of the fermentation mixture using anappropriate chemical equation.

_____________________________________________________

_____________________________________________________

_____________________________________________________

3 Explain the change in mass of the limewater using an appropriatechemical equation.

_____________________________________________________

_____________________________________________________

Check your answers.


Molar heat of combustion

Because all combustions are exothermic, DH is always a negative value.

eg. CH4(g) + 2O2(g) Æ CO2(g) + 2H2O(l) DH = – 890 kJ

The heat change DH is for the equation representing moles, in this case:

1 mol CH4 gas + 2 mol O2 gas Æ 1 mol CO2 gas + 2 mol H2O liquid

Note that DH = – 890 kJ/mol of CH4 but DH = – 445 kJ/mol of O2

1 Calculate DH per mol of CO2(g) and DH per mol of H2O (l)

_____________________________________________________

2 Do not try this. This is a ‘thought experiment’.

What would you feel if your skin is exposed to gaseous water in theform of steam that condenses to liquid water on your skin?

______________________________________________________

3 In some texts you might see the correct equation and DH value as:

CH4(g) + 2O2(g) Æ CO2(g) + 2H2O(g) DH = – 802 kJ

Explain why this correct DH value is different from the correct value

given previously as –890 kJ.

_________________________________________________________

_________________________________________________________

4 Use the information in the equations above to work out how muchheat is released when two moles of gaseous water condense to twomoles of liquid water

2H2O (g) Æ 2H2O (l) DH =

Check your answers


When you burn methane in a burner the water produced with the carbondioxide in the flame is also gas. If the gaseous products cool to theirstates at room temperature the gaseous water condenses releasing moreenergy. Heat of combustion is defined for water produced in the liquidstate.

802 kJ890 kJ

88 kJ

CH4(g)+ 2O2(g)

CO2(g)+ 2H2O(g) 2H2O(g)

2H2O(l) CO2(g)+ 2H2O(l)

CH4(g)+ 2O2(g)

Diagram illustrating DH for heat of combustion as two steps or one step

The molar heat of combustion is the heat change when one mole of thesubstance is combusted to form products in their standard states at 105 Papressure and 25°C (298 K).

1 Give the states of matter at 105 Pa and 25°C for:

a) carbon dioxide _____________________________________

b) water _____________________________________________.

2 Explain why the molar heat of combustion of methane is 890 kJ andnot 802 kJ.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

Note that when you write about a heat of combustion in a sentence it canbe given as a positive value on the understanding that all combustions areexothermic. This is demonstrated in the words of question 2 above.


If the DH is in equation form DH = is always a negative value for

combustion. Thus for methane the molar heat of combustion:

DH = – 890 kJ.

The molar heat of combustion is represented by DcH and is measured

in kJ mol–1.

For methane DcH = –890 kJ

If a table lists the heats of combustion for a number of compounds suchas alkanes the values given can be positive if the heading is –DcH

.

Alkane –DDDDcH (kJ mol–1)

methane 890

ethane 1560

propane 2220

n-butane 2877

Molar heats of combustion of alkanes (for state at 105 Pa and 25°C)

In the symbols –DcH the indicates 105 Pa (100 kPa) and 25°C.

What is indicated by

a) –

_____________________________________________________

b) c

__________________________________________________________________________________________

c) H

_____________________________________________________

d) D?

_____________________________________________________

Check your answers.


Measuring molar heat of combustion

of liquid alkanols

What you will need

Choose resources from the following

• at least three different liquid alkanols including ethanol (or methylatedspirits)

• an alcohol burner

Alkanols are flammable. Keep the bulk supply well away from the burnerand the matches.

A laboratory equipment set-up and home equipment set-up are shown on thenext page. Look at both these diagrams before looking for appropriateequipment.

• a means of measuring the mass of burner to at least 0.01 g or ameans of measuring the volume of alkanol used to 0.2 mL andidentify a data source of alkanol densities

• a container to heat 250 mL of water such as a 500 ml conical flask oran empty aluminium drink can

• a means of measuring 250 ml of water to at least the nearest 5 mL

• a thermometer measuring to at least 0.5 of a Celsius degree

• a box of matches

• a means of supporting the container of 250 mL of water about 5 cmabove the top of the burner flame.

drink can

glass tube

bark cork

wick

specimen tubealcohol

support


What you need to do:

1 Make measurements to complete the results and calculations tables.

2 You will need to devise a procedure using the resources chosen tomake the measurements. If you are not sure what to do read theActivity 4 of Part 4 of the Preliminary module Energy – determiningthe heat of combustion for some hydrocarbons.

3 Set out the procedure as a series of steps in the space for Exercise 3.2.

Results:

Alkanol ethanol

volume of water heated (mL)

mass of water heated (g)

initial burner mass (g)

final burner mass (g)

mass of alkanol used (g)

initial water temperature (°C)

maximum water temperature (°C)

change in water temperature (°C)

Alkanol Ethanol

heat released DH=

mwater x 4.18 x DT (J)

heat released/g DH/g =

DH/mass of alcohol (J)

heat release/mole =(DH/g) x molar mass

= – DcH (J)


Graph

Draw a graph of molar heat of combustion (vertical axis) versus(molecular mass). Label the axes. Draw a straight line of best fit.Extrapolate the straight line beyond the data you have measured andcalculated.

1 Explain why there is a constant difference between successive alkanolsin their molecular mass. Can you associate a particular group of atomswith this constant difference?

_____________________________________________________

_____________________________________________________

2 Explain why there is a steady increase in the molar heat ofcombustion as molecular mass increases. Can you associate aparticular group of atoms with this steady increase?

_____________________________________________________

_____________________________________________________

3 Explain why the values you calculated for molar heats of combustionare –DcH values and not –DcH

values.

_____________________________________________________

Check your answers.


Comparing practical and theoreticalvalues

The molar heat of combustion values calculated in the previous activityare based on practical measurements using simple equipment.

In the last Preliminary Module Energy Part 4 you learnt how to use bondenergy values to calculate the molar heat of combustion values forhydrocarbons. The theoretical values calculated were based on bondenergy measurements when gaseous molecules change to gaseous atoms.

Some chemists concentrate on calculations based on practicalmeasurements while other chemists concentrate on theoreticalcalculations. All chemists are trained to do practical calculations andtheoretical calculations. Many of the advances in chemistry come fromcomparing the results of practical calculations and theoreticalcalculations.

In the following activity you will compare the results of:

• your practical calculations using simple equipment,

• theoretical calculations using bond energies and

• practical calculations using equipment such as bomb calorimeters.

The sample calculation below for combustion of ethanol uses the theoreticalcalculation method from Energy Part 4.

Bond Bond energy (kJ/mol)

C–C 346

C=C 614

C C 839

C=O 804

C–O 358

C–H 414

O=O 498

O–H 463


Because bond energies are for gaseous molecules all reactants andproducts are considered as gases.

CH3CH2OH(g) + 3O2(g) Æ 2CO2(g) + 3H2O(g)

The bonds present are:

H H | |H–C – C – O–H | | H H

+ O=O Æ O=C=O + H–O–H O=O O=C=O H–O–H O=O H–O–H

Bonds broken Bonds formed

5 x C–H 4 x C=O

1 x C–C 6 x H-O

1 x C–O

1 x O–H

3 x O=O

Energy in/absorbed/DDDDH = + Energy out/released/DDDDH = –

(5x414)+346+358+463+(3x498)

= 4731

(4x804) + (6x463)

= 5994

DH = 4731– 5994 = – 1263 kJ

Heat of combustion is for:

• liquid ethanol so heat absorbed in vaporising 1 mole of ethanol = 43kJ is added to give –1263 + 43 = –1220 kJ

• formation of liquid water so heat released by condensation of 3moles of water = 3 x –44 kJ = – 132 kJ is added to give –1220 –132= –1352 kJ

Molar heat of combustion of ethanol using bond energies = –1352 kJ


Alkanol Structural formula –DDDDcH (kJ mol–1)

methanol CH3OH 726

ethanol CH3CH2OH 1367

1-propanol CH3CH2CH2OH 2021

1-butanol CH3CH2CH2CH2OH 2676

1-pentanol CH3CH2CH2CH2CH2OH 3331

1-hexanol CH3CH2CH2CH2CH2CH22OH 3984

1-heptanol CH3CH2CH2CH2CH2CH2CH2OH 4638

1-octanol CH3CH2CH2CH2CH2CH2CH2CH2OH 5294

DcH values obtained using equipment such as bomb calorimeters.

Now compare the ethanol results for the different methods.

Method Molar heat of combustion (kJ mol–1)

practical calculation, simple equipment

theoretical calculation, bond energies 1352

practical calculation, bomb calorimeter 1367

The information in this table is needed to answer Exercise 3.3.


Appendix

OPTIONAL ACTIVITY: Fermentation to make ginger beer

Wear safety goggles or glasses after you have made the ginger beer and arechecking or handling the bottles. This recipe produces about 2% v/vethanol.

You will need:

• a lemon

• sugar

• cream of tartar

• ginger root

• dried yeast

• a clean container that can hold at least 10 L of liquid such as abucket

• clean plastic bottles to hold a total of 8 L. Glass champagne bottlescould be used as these are pressure resistant. Bottles must be corkedto release pressure build up, not screw-capped.

What to do:

1 Add the juice of one lemon, 300 g of sugar, 7 g cream of tartar, 15 gof lightly crushed ginger root and 2 L of boiling water to the cleancontainer.

2 Cool to room temperature, take about 50 mL of the liquid mixtureinto a cup and stir in 7 g of dried yeast.

3 Float a slice of toasted bread on top of the mixture in the containerand pour the yeast mixture from the cup on to it.

4 Leave for a day. Remove any floating surface material with a finestrainer. Pour container liquid through the fine strainer into bottles.Cork (do not use screw caps).


5 After two days remove corks to release excess pressure buildup.

6 Leave one more day before drinking any of the ginger beer.


Suggested answers

Ethanol – a renewable resource1 C2H5OH + 3O2 Æ 2CO2 + 3H2O

2 The two main products of complete combustion of ethanol arecarbon dioxide and water.

3 Heat and light are two forms of energy released in the combustion ofethanol.

4 6CO2 + 6H2O Æ C6H12O6 + 6O2

5 Two reactants required for photosynthesis are carbon dioxide andwater.

6 Light energy is absorbed in photosynthesis.

7

ethanol glucose

sucrose

starch

cellulose

CO2

H2O

food

for organisms

fuel for

burning

photosynthesis

energy released energy absorbed

Use of ethanol as a car fuel1 The book revised in 1996 should be more up-to-date than 1992

information reprinted in 1998.

2 The 1999 revision should give information closer to current usage.


3 An .edu site usually offers more independent analysis than acommercial .com site which is more likely to have a financialinterest or a vested interest .org site.

4 Your summary should include information about:

– plant material fermented

– how ethanol is used – 10-20% anhydrous ethanol with petrol or96% ethanol with modified carburettor

– cost and subsidies compared with the fuel replaced.

5 Currently ethanol is about half the car fuel used in Brazil and anincreasing part of car fuel in the US. Both these countries haveextensive arable land and no food shortages. Countries withsubstantial oil reserves and little arable land such as around thePersian Gulf do not use ethanol. In Australia petranol, a mixture ofpetrol and ethanol, is sold near locations where ethanol is produced.

Converting plant material to ethanol1 Amylase is an enzyme which hydrolyses the polymer starch to form

the monomer glucose.

2 Cellulase is an enzyme which hydrolyses the polymer cellulose toform sugar monomers.

3 The names of enzymes usually end in the letters ‘ase’.

4 The names of carbohydrates such as glucose, sucrose, amylose andcellulose usually end in the letters ‘ose’.

5 Enzymes from yeast are used to convert glucose to ethanol.

6 The method which is used for waste wood uses the enzyme cellulaseor sulfuric acid.

7 Biomass conversion of cellulose using genetically engineered yeast.Genetic engineering involves techniques developed in the last twentyyears.

8 a) The Manildra Group use wheat starch waste left over afterextraction of protein gluten from wheat.

b) CSR at Sarina use cane sugar containing waste such asmolasses.

9 – biomass cellulose to glucose to bioethanol

– city waste contains a lot of materials based on cellulose such aspaper, cotton, plant based food

– paper and food scraps.


Fermentation1 C6H12O6 Æ 2C2H5OH + 2CO2

2 Water is the solvent required for most fermentation reactions.

3 Catalysts used in fermentation are enzymes from yeast or bacteria.

4 Distillation produces a liquid with a higher concentration of alcoholthan wine.

Monitoring mass changes in fermentation1 Decrease in mass of fermentation mixture due to loss of CO2 should

be about the same as the increase in mass of limewater by reactionwith CO2.

2 Using glucose:C6H12O6 Æ 2C2H5OH + 2CO2

Using sucrose:C12H22O11 + H2O Æ 2 C6H12O6 Æ 4C2H5OH + 4CO2

CO2 is a gas that escapes thus decreasing mass of the fermentationmixture.

3 Ca(OH)2 + CO2 Æ CaCO3 + H2O

CO2 gas absorbed increases mass of limewater.

Molar heat of combustion

1 DH = –890 kJ per mol of CO2(g) and –445 kJ per mol of H2O(l)

2 Heat released from condensation.

3 DH = –890 kJ is for formation of liquid water while DH = –802 kJ is

for formation of gaseous water.

4 The difference between DH = –890 kJ and DH = –802 kJ is the

condensation of two moles of gaseous water to liquid water releasingan extra 88 kJ. Thus 2H2O(g) Æ 2H2O(l) DH = –88 kJ

1 a) carbon dioxide gas

b) water liquid

2 Molar heat of combustion is defined for formation of water in itsstate at 105 Pa and 25°C, that is as a liquid.

a) – indicates the value is exothermic

b) c indicates combustion

c) H indicates heat

d) D indicates change.


Measuring molar heat of combustion of liquidalkanols1 Successive members of a homologous series differ by a CH2 group

thus there is a molecular mass difference of 14 between successivemembers.

2 The next member of a homologous series has an extra C and twoextra Hs to react with oxygen and release a fixed amount of energy.

3 The measurements were not all carried out at 105 Pa and 25°C.




Exercise 3.1: Ethanol as an alternative fuel

Assess (make a judgment of the value of) the potential of ethanol as analternative fuel. List the advantages and disadvantages.

Exercise 3.2: Procedure used to measure DDDDcH of

liquid alkanols


Exercise 3.3: Comparing practical and theoreticalvalues

Method Molar heat of combustion (kJ mol–1)

practical calculation, simple equipment

theoretical calculation, bond energies 1352

practical calculation, bomb calorimeter 1367

Suggest reasons why the practical calculation using simple equipmentusually gives a different result from the other methods.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Gill Sans Bold



Part 4: Galvanic cells – electrical energy from materials


AMENDMENTS

��Cu rod

porous pot

Zn cylinder

Zn2+ Cu2+ Cu2+ Zn2+

1850s Daniell cell

graphite cathode

cathode mix ofMnO2 and C

zinc anode

electrolyte paste ofNH4Cl and ZnCl2

1900s dry cell

2 V

cathodePbO2

anodePb

PbO2Pb (spongy)

12 V

2 V

cathode anode

1900s lead-acid cell

1990s fuel cell

��external circuit

anod

e

cath

ode

e– e–

O2H2CO3

2– CO2

H2O

molten carbonateelectrolyte

porous carbonelectrodes containing

metal catalysts

organo-ruthenium dye

absorbed on

e–

I3– + 2e– 3I–

2Dye+ + 3I– 2Dye + I3–

2Dye 2Dye+ + 2e–e– e–

lightglass insulatortransparentconducting layer

semiconductor TiO2

e– e–

I– I3–

glass insulator

transparentconducting layer

e–

2000s liquid junction photovoltaic cell

Part 4: Galvanic cells – electrical energy from materials 1

Contents

Introduction ............................................................................... 3

Metals and electrons ................................................................. 5

Displacement of metals from solution .................................................7

Oxidation and reduction ............................................................ 9

Oxidation/reduction reactions ..............................................................9

Oxidants and reductants ....................................................................10

Oxidation state....................................................................................13

Galvanic cells .......................................................................... 15

Investigation of galvanic cells ............................................................16

What is a galvanic cell? .....................................................................18

Daniell cell ..........................................................................................21

Measurement of standard potentials ....................................... 23

Predicting potential differences .........................................................25

Sources of electrochemical energy ......................................... 28

Primary (non-rechargeable) batteries ...............................................28

Secondary (rechargeable) batteries..................................................30

Flow batteries .....................................................................................32

Appendix ................................................................................. 35


Suggested answers ................................................................. 37

Exercises – Part 4.................................................................... 41


Introduction

Galvanic cells are important in releasing energy in its most useful form –as electricity (electrical energy) – from materials. Electricity is the mostversatile form of energy, easily converted into kinetic energy, heat, light,chemical energy and sound. Furthermore, modern communicationmethods and information storage and retrieval, are based on theavailability of electrical energy. If a source of electrical energy needs tobe compact and portable, galvanic cells in the form of batteries areusually the first choice.

The oxidation-reduction or electron transfer reactions that you will studyin this part are increasingly important as a source of energy. Imagineliving without all the battery operated devices that are part of your everyday life.

Electron transfer reactions that you will study also occur in thephotosynthesis that changes light energy to chemical energy, therespiration reactions in cells that provide energy for life and thecombustion reactions that provide humanity with most of its energy.


• explain the displacement of metals from solution in terms of transferof electrons

• identify the relationship between displacement of metal ions insolution by other metals to the relative activity of metals

• account for changes in the oxidation state of species in terms of theirloss or gain of electrons

• describe and explain galvanic cells in terms of oxidation/reductionreactions

• outline the construction of galvanic cells and trace the direction ofelectron flow

• define the terms anode, cathode, electrode and electrolyte to describegalvanic cells.



• perform a first-hand investigation to identify the conditions underwhich a galvanic cell is produced

• perform a first-hand investigation and gather first-hand informationto measure the difference in potential of different combinations ofmetals in an electrolyte solution

• gather and present information on the structure and chemistry of adry cell or lead-acid cell and evaluate it in comparison to one of thefollowing:

– button cell

– fuel cell

– vanadium redox cell

– lithium

– liquid junction photovoltaic device (eg. the Gratzel cell)

in terms of:

– chemistry

– cost and practicality

– impact on society

– environmental impact

• solve problems and analyse information to calculate the potentialE requirement of named electrochemical processes using tables ofstandard potentials and half equations.




Metals and electrons

In the module, Metals, you learnt that:

• a metal atom has a small number of electrons in its outer valenceshell

• when a metal atom M reacts it usually loses all its outer valence shellelectrons to form a cation: M Æ Mn+ + ne–

• metals vary in their reactivity and can be arranged in a metal activityseries from most active to least active:

K Na Li Ba Ca Mg Al Cr Zn Fe Co Ni Sn Pb Cu Hg Ag Pt Au

• metal reactions with other chemicals can be summarised using themetal activity series:

K Na Li Ba Ca Mg Al Cr Zn Fe Co Ni Sn Pb Cu Hg Ag Pt Au

dilute acids react

water reacts

oxygen fast

alkali

steam reacts

oxygen slow reaction very slow

alkali

• equations can be written as full formula equations Mg + 2HCl Æ MgCl2 + H2

or as net ionic equations Mg + 2 H+ Æ Mg2+ + H2

• the equation for a the reaction of a metal with an acid ( H+ ) can beexpressed as two half equations:

M Æ M2+ + 2e–

2 H+ + 2e– Æ H2

________________________________

M + 2 H+ Æ M2+ + H2


• the coefficients of a balanced equation show the mole relationshipbetween reactants and products

M + 2 H+ Æ M2+ + H2

1 mol + 2 mol Æ 1 mol + 1 mol

Revision of aspects of electrochemistry1 Write a half equation to show formation of a copper(II) ion from

copper.

_____________________________________________________

2 Write a half equation to show formation of an Al3+ from Al.

______________________________________________________

3 Write a full formula equation to show the reaction of magnesiummetal with oxygen gas to form ionic magnesium oxide MgO.

______________________________________________________

4 Write a full formula equation to show the reaction of magnesiumwith sulfuric acid H2SO4 to form magnesium sulfate MgSO4 salt anda gas.

______________________________________________________

5 In the equations for questions 3 and 4 above the magnesium atomundergoes a reaction that can be written as a half equation. Write thehalf equation for the change that occurs to magnesium atoms.

______________________________________________________

6 Two moles of aluminium reacts with six moles of hydrochloric acidto form two moles of aluminium chloride AlCl3 and three moles ofhydrogen gas. Express this information as a balanced equation.

______________________________________________________

7 Write the half equation in which a lithium atom forms a Li+.

______________________________________________________

8 Write the half equation in which hydrogen ions form hydrogen gas.

______________________________________________________

9 Combine the two half equations from questions 7 and 8 to get anionic equation for the reaction of lithium metal with acid.

______________________________________________________

Check your answers.


Displacement of metals from solution

The simplest way to make a solution containing a particular metal ion isto dissolve one of its salts in water. All nitrate and acetate salts are watersoluble, as are most chlorides (exceptions: Ag+, Pb2+) and most sulfates(exceptions: Ba2+, Ca2+, Pb2+, Ag+).

If a variety of metals are immersed in a variety of metal salts and theresults tabulated in order of metal activity a pattern can be demonstrated.

+ = reaction – = no reaction

Metals

Mg Zn Fe Pb Cu Ag

Mg2+ – – – – – –

Zn2+ + – – – – –

Fe2+ + + – – – –

Pb2+ + + + – – –

Cu2+ + + + + – –

Metalions

Ag+ + + + + + –

1 The results show that when a metal is placed in a solution of its ownions _________________________________________________

2 The most reactive metal in this table is ______________

3 The least active metal in this table is ______________

4 An active metal reacts with less active _______ ions.

5 The most reactive metal ion in this table is the _____________ ion.

6 The least reactive metal ion in this table is the _____________ ion.

7 If a metal atom is very reactive then its ion is much _____ reactive.

Check your answers.


Observing the reaction between iron atoms andcopper(II) ions

What you need:

• iron nail (if rusty, clean surface with iron wool)

• solution of copper(II) ions eg. copper(II) sulfate solution or a solution ofcopper(II) acetate prepared by dissolving copper carbonate in vinegar;copper that has been exposed to the atmosphere (but not near salt water)for a long time can be covered with green carbonate

• small transparent container to hold the nail partly in and partly out ofthe solution.

What you will do:

1 Pour the copper(II) solution into the container

2 Position the iron nail partly in and partly out of the solution

3 Observe and record observations after 5 minutes, an hour and a day.In particular note any colour changes.

Results:

Conclusions:

1 Number the statements below into a sequence to explain yourobservations.

• A solution of light green Fe2+ ions is oxidised by oxygen from theair to yellow Fe3+ ions.

• The part of the iron nail in the solution becomes thinner as ironatoms Fe dissolve to form light green iron(II) ions Fe2+

.

• The blue solution of copper(II) ions loses colour as blue Cu2+ ionsreact to form dark metallic copper Cu.

2 Write a balanced equation underneath the word equation:

iron atoms + copper ions Æ iron ions + copper atoms

Check your answers.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Oxidation and reduction

Oxidation/reduction reactions

An oxidation/reduction reaction involves electron transfer from oneparticle (atom, molecule or ion) to another particle (atom, molecule orion). eg. from iron atom to copper(II) ion in Fe + Cu2+ Æ Fe2+ + Cu

Oxidation is loss of electrons. mnemonic: OIL = Oxidation Is Loss

Reduction is gain of electrons mnemonic: RIG = Reduction Is Gain

Sorting oxidation and reduction half equations. As you read the followinghalf equations from left to right you should be able to decide whichrepresent oxidation and which represent reduction. Place OX after anoxidation half equation and RED after a reduction half equation.

Mg2+ + 2 e– Æ Mg

Zn2+ + 2 e– Æ Zn

Cu Æ Cu2+ + 2 e–

Cu2+ + 2 e– Æ Cu

Mg Æ Mg2+ + 2 e–

Ag Æ Ag+ + e–

Fe2+ + 2 e– Æ Fe

Pb2+ + 2 e– Æ Pb

Pb Æ Pb2+ + 2 e–

Zn Æ Zn2+ + 2 e–

Fe Æ Fe2+ + 2 e–

Ag+ + e– Æ Ag


Explain why oxidation-reduction reactions can be called:

a) redox reactions

_____________________________________________________

_____________________________________________________

b) electron transfer reactions

_____________________________________________________

_____________________________________________________

Check your answers.

Oxidants and reductants

When a redox reaction occurs the reduction (gain of electrons) andoxidation (loss of electrons) occur simultaneously (at the same time).

eg. Fe + Cu2+ Æ Fe2+ + Cu

An iron atom transfers two electrons to a copper ion. This produces aniron(II) ion and a copper atom.

Fe

Cu2+

Fe2+

Cu2+

Fe

Cu

2e–

Cu2+

Cu2+

Cu2+

Cu2+

The chemical species that causes the oxidation (loss of electrons) iscalled the oxidising agent or oxidant. Cu2+ has caused the iron atom tolose two electrons so in this reaction Cu2+ is the oxidant.

The chemical species that causes reduction (gain of electrons) is calledthe reducing agent or reductant. Fe has caused the copper(II) ion to gaintwo electrons so in this reaction Fe is the reductant.


When the reaction is expressed as two half equations

Fe Æ Fe2+ + 2 e– the oxidation half equation showing loss ofelectrons shows the reductant undergoing oxidation.

Cu2+ + 2 e– Æ Cu the reduction half equation showing gain ofelectrons shows the oxidant undergoing reduction.

Fe + Cu2+ Æ Fe2+ + Cureductant oxidant

Every redox reaction requires a species able to donate electron(s)– the reductant – and a species able to accept electron(s) – the oxidant.

You must learn to use the terms oxidation, reduction, oxidant and reductantcorrectly and frequently to progress in your study of electrochemistry.Complete the table then check your answers.

Reaction Oxidation Reduction Oxidant Reductant

Mg+Zn2+ ÆMg2++Zn Mg ÆMg2++2e– Zn2++2e– ÆZn Zn2+

Zn+Cu2+ ÆZn2++Cu Zn ÆZn2++2e– Zn

Mg+2H+ ÆMg2++H2 2H++2e– ÆH2 H+

From the examples of redox reactions you have studied so far you mayalready realise that:

• metals can act as reductants

• positive metal ions can act as oxidants.

Reacting zinc and iodine

This activity requires:

• finely divided zinc Zn(s); this can be obtained by shaking out powderfrom the bottom of a plastic bag that contained galvanised nails or byrunning a metal file down the side of a galvanised nail many times.

Make sure the galvanised nails are not labelled with the word cadmium –cadmium is a very toxic metal.

• a dilute iodine solution I2(aq); prepared by adding one drop of iodinetincture to every two millilitres of water

• a small test tube to hold the iodine solution.


Add some of the finely divided zinc to the iodine solution and shake.Wait for the zinc particles to settle then observe if the iodine solution haschanged colour. If there is no colour change shake again or add morefinely divided zinc.

If zinc acts as a reductant write an oxidation half equation for its reaction.

_________________________________________________________

If zinc was the reductant what chemical was the oxidant? Write areduction half equation for the oxidant reaction:

_________________________________________________________

Add the two half equations to obtain a full equation:

_________________________________________________________

Check your answers.

This reaction demonstrates that non-metals such as a halogen, as well asoxygen, can react as oxidants.

In the halogen group the order of oxidant strength is:

fluorine > chlorine > bromine > iodine.

Half equations for halogen/halide ion reaction can be arranged in order:

weaker oxidant 1/2I2(aq) + e– I– stronger reductant

1/2Br2(aq) + e– Br–

1/2Cl2(aq) + e– Cl–

strongest oxidant 1/2F2(g) + e– F– weakest reductant

Note that halide ions act as reductants in the reverse order:

iodide > bromide > chloride > fluoride.

Half equations for metal ion/metal reaction can also be arranged in order:

weaker oxidant Mg2+ + 2e– Mg stronger reductant

Zn2+ + 2e– Zn

Fe2+ + 2e– Fe

stronger oxidant Cu2+ + 2e– Cu weaker reductant

Later on you will see how non-metal and metal half equations can bebrought together in a single table of reduction potentials.


Oxidation state (oxidation number)

Oxidation states (or numbers) are positive or negative numbers allocatedusing agreed rules. They have been used to widen the definition ofoxidation and reduction so that:

• oxidation is an increase in oxidation number

• reduction is a reduction in oxidation number.

-5 -4 -3 -2 -1 0 1 2 3 4 5

reduction

oxidation

Any equation where you can show a change in oxidation number can beregarded as a redox equation.

Rules for allocating oxidation number (OxN)

• 0 for atoms in elements eg. Mg, O2

• equal to the charge of a monatomic ion eg. 2 for Mg2+, –1 for I–

• –2 for oxygen (except in peroxides such as H2O2 where OxN = –1)eg. such as

• 1 for hydrogen (except in metal hydrides such as Li+H– where H– hasOxN = –1)

• the algebraic sum of OxNs in a molecule must be zero eg. H2O(2 x 1 for two hydrogens) + (–2 for oxygen) = 0

• the algebraic sum of OxNs in an electrically neutral formula for anionic compound must be zero eg. Ca(OH)2 2 for Ca2+ + 2 x –2 fortwo oxygens + 2 x 1 for two hydrogens = 2 – 4 + 2 = 0

• the algebraic sum of OxNs in a polyatomic ion is equal to the chargeon the ion eg. in NH4

+, N must have OxN = –3 so that –3 +(4 x 1)=+1; in NO3

–, N must have OxN = 5 so that 5 +(3 x –2) = –1

Changes in the oxidation state of a species can be accounted for in termsof an imagined loss or gain of electrons.

In NH4+ the fact that N has an OxN of –3 does not mean the N atom has a

charge of –3. N is just more electronegative than H and can be imaginedto attract three electrons more strongly than three of the hydrogens ( thefourth H has no electron as it attached to a NH3 molecule as a H+ ion ).

In NO3– the N is less electronegative than O and can be imagined to

attract its five valence shell electrons less strongly than the oxygens do.Thus in NO3

– the N has an OxN of +5.


The OxN does not indicate the presence of positive and negative ions. Itis simply a tool or accounting device that enables you to work out if anelement has been oxidised or reduced.

Oxidation numbers are particularly useful for determining if a fullformula equation represents a redox reaction.

eg. CH4 + 2O2 Æ CO2 + 2H2O

In CH4 carbon has an OxN of –4 while in CO2 its OxN is +4. Thisincrease from –4 to +4 indicates the carbon has undergone oxidation.The oxygen on the LHS is in the element with OxN = 0 while the O inthe compounds CO2 and H2O has OxN = –2. This reduction in OxNindicates oxygen has undergone reduction. This must be a redox reactionin which the C is oxidised and the O is reduced.

In the precipitation Ag+ + NO3– + Na+ + Cl– Æ AgCl(s) + Na+ + NO3

–

OxNs are 1 5 –2 1 –1 1 –1 1 5 –2Because no OxNs change this is not a redox reaction.

Write the oxidation numbers under each element in the equations below.The first two are examples of what to do. If you are not sure why a certainOxN is allocated then read through the rules for allocating OxN again.Check that the equations are balanced by comparing the total OxN on theLHS with the RHS

1 Fe + Cu2+ Æ Fe2+ + Cu 0 2 2 0 0 + 2 = 2 + 0

2 Mg + 2Ag+ Æ Mg2+ + 2Ag 0 1 2 0 0 + 2 x 1 = 2 + 2 x 0

3 Mg + 2H+ Æ Mg2+ + H2

4 Mg + 2HCl Æ MgCl2 + H2

5 2Mg + O2 Æ 2MgO

Check your answers.



energyinteractions

H2O


formulasequations

calculations

particlesenergy

interactions


formulasequations

calculations

OH

H

OH

HOH

H

OH

H

Galvanic cells

Luigi Galvani was an Italian professor of anatomy whose investigationsin the late 1700s led to major advances in physics and biology as well aschemistry. He found that the muscle fibre of frog legs would contractwhen the connected nerves were touched with a source of staticelectricity. This led to the idea that electricity in the nerves of animalsstimulated muscle action. In later experiments he found a greaterresponse when the nerve was touched with two different metals and heconstructed a crude source of electricity from two different metals andfluid from a dissected frog.

This development of a source of electric current was extended by theItalian physicist Alessandro Volta in 1800. He constructed a cell madeof silver and zinc disks separated by cardboard soaked in salt water.By piling the cells on top of one another he produced a pile (known asVolta’s pile)which was the first source of continuous electricity. Pilesof cells (batteries) provided the technology used to separate newelements from compounds and stimulated the development of versatileways of using electric energy.

Use a dictionary to match words derived from Galvani and Volta –galvanise, galvanometer, volt, voltage, voltmeter and voltameter – withmeanings.

Term Meaning

coat with zinc

potential difference or electromotive force

instrument measuring voltage

unit of potential difference or electromotive force

instrument measuring small currents

measures quantity of electricity by decomposition

Check your answers.


A galvanic or voltaic cell is a device for delivering an electric currentproduced by a chemical reaction. Such a device is commonly called abattery. Strictly a battery is a series of cells joined together to provide ahigher voltage. In practice single cells that give between 1 and 2 V areoften labelled as batteries. Six 2 V cells in series produce a 12 V carbattery while six 1.5 V cells in series make up a 9 V battery.

battery of six cellsjoined in series

single cell

Investigating galvanic cells

1 Making a galvanic cell

What you will need:

• two different metals eg. steel paper clip and brass drawing pin or zincgalvanised nail and copper wire

• an electrolyte solution eg. a citrus fruit juice solution such as in alemon which has been rolled and massaged by hand to enable the citricacid solution to move freely; cut the fruit in half or a solution of acidsuch as vinegar in a container

• to detect the current produced you will need a multimeter able tomeasure to at least 0.2 V DC or, since you are dealing with a very lowvoltage source, you can use a sensitive moist tongue.

If you do not have the required equipment but have an amalgam filling inone of your teeth you could do the activity described in the box belowinstead. This only requires some aluminium foil.

What you will do:

Set up the two metals so that they are not touching but are close andimmersed in an electrically conducting electrolyte solution.

If you are using a multimeter place a probe on each of the metals. If themultimeter is read by a needle moving over a scale and the needle movesaway from the scale then swap the probes over.

If you are using your tongue, lightly touch the moist tip to form a 'bridge'between the two metals. If you do not notice anything moisten yourtongue again and try another part of your tongue.


tongue

brass drawing pin

lemon skinlemon juice

steel paper clip

If you have a metal tooth filling and a piece of aluminium foil you cancreate a galvanic cell in your mouth. The saliva in your mouth acts as anelectrolyte solution. When you successfully create a galvanic cell in yourmouth you will know from the electricity travelling along a nerve! If youare very sensitive or do not have a metal filling you may like to seek outa friend to help you.

If you are pain resistant and devoted to advancing scientific knowledgeyou might like to investigate:

• positioning of the aluminium foil

• whether having some table salt dissolved in saliva on the top of atooth increases the effect.

saliva electrolyte

galv

anic

cel

l

Al Al3+ + 3e–

short circuit

inert amalgam(Ag + Sn + Hg)

O2 + 4H++ 4e–

2H2O nerveto

brain

pulse ofelectricity

2 Measuring the difference in potential betweendifferent metals

What you will need:

• A variety of metals such as steel paper clip, brass drawing pin,copper wire, iron nail, zinc galvanised nail, silver plated cutlery,nickel plated jewellery.

• An electrolyte solution to place the metals in e.g. vinegar (5%w/wacetic acid solution) or a salt solution (make about 5%w/w salt).

• Multimeter able to measure to at least 0.2 V DC (direct current).


What you will do:

1 Place the different metals the same distance apart. Measure thepotential (voltage) difference between pairs of different metals.

2 What happens when the two metals are the same?

3 Which metal combination gives the greatest voltage?

zinc (galvanised) silver (plated)

VD.C.

Measuring the difference in potential between zinc and silver.

Conclusions:

From the results of your first-hand investigations you should be able tocomplete the sentences below:

To produce a galvanic cell the following are required:

• two different ___________ which cannot be touching

• an ____________ solution (conducting solution) in which ions arefree to move and so conduct electric charge.

• For a galvanic cell to provide a useful flow of electrons the two___________ need to be connected by a conducting wire.

Check your answers.

What is a galvanic cell?

A galvanic cell physically separates a reductant and an oxidant so thatelectrons cannot go directly from the reductant to the oxidant. Insteadthe electrons must move along an electrical conductor such as a copperwire connecting the reductant half with the oxidant half of the cell.The moving electrons can be used to produce kinetic energy with anelectric motor, heat and light energy with a light globe, and other energyconversions.


The simplest galvanic cell consist of two different metals in contact withan electrolyte solution. If the two different metals are joined by anelectrical conductor electrons flow from the more active metal to the lessactive metal.

e–e–

metals + electrolyte different metals joined external circuit electron flow internal circuit ion flow

A buildup of negative charge on the silver spoon and a buildup ofpositive charge on the zinc coated nail would quickly prevent furtherflow of electrons in the external circuit. Flow of ions in the electrolyteinternal circuit cancels negative charge on the silver and positive chargeon the zinc. Electron flow continues in the external circuit as long as ionflow is possible in the internal circuit.

Another galvanic cell arrangement uses the two different metals in twodifferent containers of their ions. To complete the electric circuit anelectrically conducting salt bridge is used. The salt bridge can be a filterpaper or cotton wool soaked in a salt solution such as potassium nitratesolution. K+ and NO3

– ions moving through the water solution allowflow of electric charge between the two containers.

e–

Zn

Zn2+ Ag+

Ag NO3– K+ NO3

– K+

no external circuit no external circuit external circuit complete

no internal circuit internal circuit complete internal circuit complete


Electrodes

The material transferring electrons to or from an electrolyte solutions iscalled an electrode.

Metals and graphite are used as electrodes because they are goodelectrical conductors.

Would you use a metal of high, medium or low activity for an electrode in awater solution? Give a reason in your answer.

_________________________________________________________

_________________________________________________________

Check your answer.

The electrodes need to be connected by an electrolyte which can transferelectric charge, usually by the movement of positive cations and negativeanions in solution. The solution may be in a paste (as in a dry cell, that isconventional battery) or gel or porous solid designed to minimisemovement of the liquid contents.

The electrolyte used in salt bridges is usually potassium nitrate becauseall K+ and all NO3

– salts are soluble. When these ions move into the twocontainers joined by the salt bridge they do not react with any other ionsto form insoluble precipitates.

The anode is always defined as the electrode at which oxidation occurs.

The cathode is always defined as the electrode at which reductionoccurs.

The oxidation at the anode involves loss of electrons to the externalcircuit. Thus the anode acts as a source of negative electrons and so ismarked – in a battery (galvanic cell). The loss of electrons leaves theanode region positive so that it attracts negative anions in the electrolyte.

The reduction at the cathode involves gain of electrons from the externalcircuit. Thus electrons move from the anode, marked – , through theexternal circuit to the cathode, marked + , in a battery (galvanic cell).This gain of electrons by the cathode region makes it negative so that itattracts positive cations in the electrolyte.

While electrons are moving through the external circuit ions are movingbetween the electrodes inside the cell. The movement of anions to theanode and cations to the cathode inside the cell completes the electriccircuit. Electrons cannot move through water or electrolyte solutions.


Galvanic cell releasing electrical energyconductor wire external circuit

electron flow

+ cations

– anions

electrolyte internal circuit

cathodeanode

marked – marked +

Oxidation Reduction

loss of electronsmakes this region positive

gain of electrons makesthis region negative

Do you remember the mnemonic OIL RIG for oxidation is loss (ofelectrons) and reduction is gain (of electrons)? Successfulchemistry students know a number of mnemonics, some they havelearnt from other people while other mnemonics have been createdby the students to aid their memory. Here are some additionalmnemonics to help you.

AN OX (first two letters of anode and oxidation) and RED CAT(first two letters of reduction and cathode) are mnemomics to helpyou remember the anode and cathode definitions.

An alternative mnemonic is:anode and oxidation both start with vowels (a and o)cathode and reduction both start with consonants (c and r).

Always remember that for any cell involving electrical energy:

ANode OXidation REDuction CAThode

Daniell cell

The Daniell cell was developed in 1836 and provided most of theelectricity used in the 1800s to operate extensive morse code telegraphsystems and the first telephone systems. This cell uses the reactionbetween zinc metal and copper sulfate.

The physical arrangement of reactants can be represented as Cu | Cu2+ ||Zn2+ | Zn using a convention agreed to by IUPAC. The single verticalline represents the boundary between phases, in this case solid andsolution; the double vertical line represents a salt bridge or a porousbarrier through which ions can move to complete an electrical circuit.


The Cu|Cu2+ and Zn2+|Zn arrangements are called half cells.

Reduction occurs in the copper half cell: Cu2+ + 2e– Æ Cu

Oxidation occurs in the zinc half cell: Zn Æ Zn2+ + 2e–

A galvanic cell always has a reduction half cell and an oxidation halfcell.

In the Daniell cell the zinc is called an active electrode because itactually reacts and gradually dissolves. The copper is an inert electrode;it becomes thicker as copper atoms are deposited on its surface.

Cu rod

porous pot

Zn cylinder

Zn2+ Cu2+ Cu2+ Zn2+

Daniell cell used in the 1800s:

ZnCu

Cu2+ Zn2+

salt bridge

Daniell cell set up in a schoollaboratory


Measurement of standard potentials

The potential of a chemical to undergo reduction or oxidation can bemeasured electrically.

If the measurements are carried out under standard conditions –temperature 25°C, gases at 105 Pa pressure and solution concentrations 1mol L–1. The values obtained are called standard potentials. Thenumerical values are expressed compared to a hydrogen electrode. Ahydrogen electrode Pt[H2(g)] | 2H+ consists of hydrogen gas at 105 Papressure bubbling over a platinum electrode in a 1 mol L–1 H+ solution.

Any chemical which is an electrically conducting solid can act as anelectrode eg. the zinc metal and the copper metal in a Daniell cell.

If the oxidant or reductant is a liquid, gas or in solution, it is placed incontact with an inert conducting electrode such as platinum, graphite orstainless steel. Electrons can be lost or gained by the liquid, gas orsolution chemicals through the electrode.

Zn

Zn2+

salt bridgeH2 gas

-0.76

H+ H+

1M HCl 1M ZnSO4

Pt[H2(g)] | 2H+ || Zn2+ | Zn cell

Cu

Cu2+

salt bridgeH2 gas

+0.34

H+ H+

1M HCl 1M CuSO4

Pt[H2(g)] | 2H+ || Cu2+ | Cu cell

Standard potential measurements made using different half cells joined toa hydrogen electrode half cell can be organised into a table. View thetable now by turning to the Appendix.


In other texts you may find the order of the equations inverted but the E∆

values should be the same voltage for the same equation in this table.

Knowing that active metals such as lithium and potassium are strongreductants write ‘strong reductants’ at the top right hand corner of thetable. Going down the right hand side the reductants become weaker.Write ‘weak reductants’ at the bottom right hand corner.

Knowing that active non-metals such as fluorine, chlorine and oxygen arestrong oxidants label the ‘strong oxidants’ and ‘weak oxidants’ corners ofthe left hand side of the table.

Check your answers.

The table can be used to predict whether a reaction is likely to occur.

Consider the reaction of acids containing H+ with metals to release H2

gas. H+, a moderate oxidant will react with any reductant above it on theRHS of the table. Thus metals from Pb upwards on the RHS arepredicted to react with acids releasing hydrogen gas. Copper is below H+

and is predicted not to react; experiments verify that copper does notdisplace hydrogen gas from acid solutions.

A metal will react with ions of a less active metal. Note that:

• going down the RHS of the table the metals decrease in reductantstrength

• going down the LHS of the table the metal ions increase in oxidantstrength.

The layout of the table you are using has

weak oxidant + electron(s) strong reductantmoderate oxidant + electron(s) moderate reductant

strong oxidant + electron(s) weak reductant

Use the table to predict what will happen when the reactants below aremixed. If you predict no reaction write no reaction after the arrow. If youpredict reaction then complete the equation and balance it.

1 Ag + H+ Æ

2 Ni + Ag+ Æ

3 Na + H2O Æ

Check your answers.


Predicting potential differences

The voltage obtainable from a galvanic cell can be predicted using thetable of standard potentials.

Consider the Daniell cell Cu | Cu2+ || Zn2+ | Zn where the half cellreactions are Cu2+ + 2e– Æ Cu and Zn Æ Zn2+ + 2e– .

The table equations are provided in the format oxidant + e– Æ reductant.

The equation Zn Æ Zn2+ + 2e– is the reverse of this format and so itsE∆ value has to have its sign reversed giving

Zn Æ Zn2+ + 2e– +0.76 volts

Adding the two half equations and their E∆ values, one for oxidation and

the other for reduction, gives the full equation and predicted cell voltage.Add the LHSs, put in the arrow, then add the RHSs. Cancel anythingthat is common to both sides of the equation, in this case 2e–.

Zn Æ Zn2+ + 2e– +0.76 volts

Cu2+ + 2e– Æ Cu 0.34 volts________________________________

Zn + Cu2+ + 2e– Æ Zn2+ + Cu + 2e– 0.76 + 0.34 = 1.10 volts

Often you will need to multiply a half equation by 2 or 3 so that thenumber of electrons is the same when adding the oxidation and reductionhalf equations together. When you do this the half cell voltages do notchange. The voltage is a property of the reactant that does not depend onthe number of particles.

For example the reaction of aluminium with copper(II) ions.

2 x ( Al Æ Al3+ + 3e– ) +1.68 V

3 x ( Cu2+ + 2e– Æ Cu ) 0.34 V__________________________________

2 Al + 3 Cu2+ + 6e– Æ 2 Al3+ + 3 Cu + 6e– 2.02 V for the cell

A galvanic cell reacting aluminium metal and copper(II) ions is predictedto produce 2.02 volts. In practice the voltage obtained would probablybe a little different. This could be due to conditions other than standard,impure metal, surface coating of oxide on metal, and so on.


When addition of two half cell E values gives a positive cell voltage thereaction is expected to occur spontaneously. The cell is a galvanic cell inwhich chemical energy is changed to electrical energy.

If the addition of half cell values gives a negative cell voltage thereaction will not occur spontaneously. For the reaction to occur electricalenergy has to be put into the cell arrangement. The cell needs to becomean electrolysis or electrolytic cell. Any electrical energy put in changesto chemical energy. The voltage of electrical energy applied to the cellfor reaction to occur has to be greater than the calculated voltage.

Consider the electrolysis of water to produce hydrogen and oxygen.

water Æ hydrogen + oxygen

2H2O Æ 2H2 + O2

The relevant half cell equations are

H2O + e– Æ 1/2H2 + OH– –0.83 V

H2O Æ 1/2O2 + 2 H+ + 2e– –1.23 V

Multiplying the top equation by two and adding gives:

2H2O + 2e– Æ H2 + 2OH– –0.83 V

H2O Æ 1/2O2 + 2 H+ + 2e– –1.23 V________________________________________________3H2O + 2e– Æ H2 + 1/2O2 +2H+ + 2OH– + 2e– –2.06 V

The H+ and OH– on the RHS react to form water H++ OH– ÆH2O giving

3H2O + 2e– Æ H2 + 1/2O2 +2H2O + 2e– –2.06 V

Removing 2H2O from the LHS and RHS simplifies to

H2O Æ H2 + 1/2O2 –2.06 V

It is preferable to have whole number coefficients in an equation so:

2H2O Æ 2H2 + O2 –2.06 V

Note that during all this manipulation of equations the cell voltage doesnot change from – 2.06 V.

The negative value indicates that water decomposing to hydrogen andoxygen does not occur spontaneously. A voltage greater than 2.06 V hasto be applied before decomposition of water occurs.


Shortcut method

The voltage of a galvanic cell (a positive voltage) or the voltage neededto be exceeded to operate an electrolysis cell (a negative voltage) canoften be worked out by inspection of the table of electrode potentials.

Example 1: What voltage can be obtained from a cell using magnesiumand zinc half cells?

The E∆ values for magnesium and zinc half cells are –2.36 and –0.76

volts. The difference between these two values is 1.60 volts.

Mg2+ + 2e– Mg –2.36

Zn2+ + 2e– Zn –0.76

difference1.60

Magnesium is the more active metal and so will act as the reductant,undergo oxidation and thus be the anode. Zinc ions will undergoreduction at the zinc metal cathode.

Example 2: What voltage can be obtained from a cell using silver andcadmium half cells?

Cd2+ + 2e– Cd –0.40

Ag+ + e– Ag 0.80

difference1.20

Example 3: What is the maximum voltage that could be obtained fromchemicals shown in the table of standard potentials?

A cell reacting lithium and fluorine in theory could provide a voltageequal to the difference between –3.04 and 2.89 volts, that is 5.93 volts.

In practice such a cell would be difficult to construct as lithium reactswith oxygen and water while fluorine reacts with most substances withwhich it makes contact. There is another way of getting higher voltages.

Most cells give one to two volts. By arranging cells in series the cellvoltages are added together. A 9 V battery is a series of six 1.5 V cells.


Sources of electrochemical energy

Primary (non-rechargeable batteries)

Primary cells are meant to be used until all available chemical energy hasbeen changed to electrical energy then discarded properly.

Dry cell / Leclanche cell / Zn-C / Zn-MnO2 (1.5 V)

These are low cost and safe to use but have poor performance at lowtemperatures.

graphite cathode

cathode mix ofMnO2 and C

zinc anode

electrolyte paste ofNH4Cl and ZnCl2

Anode reaction: Zn Æ Zn2+ + 2e–

In the cathode reaction a manganese compound with oxidation state 4(IV in roman numerals) is changed to a manganese compound withoxidation state 3 (III in roman numerals). Half equations with complexreactions like this will be simplified to:

Cathode reaction: Mn(IV) + e– Æ Mn(III)

The heavy duty variety of dry cell uses higher quality synthetic MnO2

and an electrolyte paste of the more expensive ZnCl2. This enables ahigher current and better low temperature performance.


The alkaline variety of dry cell has a 7 M KOH electrolyte paste anddifferent electrode reactions:

Anode: Zn + 2OH– Æ ZnO + H2O + 2e–

Cathode: Mn(IV) + 2e– Æ Mn(II)

Alkaline cells are most efficient providing moderate continuous currents,have good low temperature performance, maintain a steady voltage andhave a longer shelf life. However they are more expensive.

Button cell / Zn-Ag2O (1.6 V)

insulation

KOHelectrolyte

pasteAg2O

powdered zinc

steel can

Anode: Zn + 2OH– Æ ZnO + H2O + 2e–

Cathode: Ag2O + H2O + 2e– Æ 2Ag + 2OH–

Mercury button cells previously available are no longer producedbecause of obsolete technology and concern about release of mercuryinto the environment.

Lithium iodine button cells are used for heart pacemakers. Theelectrolyte is a conducting polymer containing Li+I– formed between theanode and cathode.

Anode: Li Æ Li+ + e–

Cathode: 1/2I2 + e– Æ I–

Lithium batteries using Li and FeS2 are now available. These deliver 1.5V, weigh less than an alkaline battery, deliver up to five times the powerbut are very expensive.

Use a table of atomic weights to explain why a 1.5 V lithium battery weighsmuch less than a 1.5 V dry cell.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.


Secondary (rechargeable) batteries

These can be discharged and recharged hundreds or thousands of times.The average car battery lasts three to five years. Eventually the physicaland chemical changes involved break down the structure of the battery.

Lead-acid cell (2.0 V)

12 V car batteries are made up of six 2 V lead-acid cells. Lead gridplates of spongy lead and lead(IV) oxide are immersed in a 4 to 5 Molarsulfuric acid solution.

2 V

cathodePbO2

anodePb

PbO2Pb (spongy)

12 V

2 V

cathode anode

Anode: Pb + SO42– Æ PbSO4 + 2e–

Cathode: PbO2 + 4H+ + SO42– + 2e– Æ PbSO4 + 2H2O

The larger the number of plates in a cell the larger the surface area forreaction. This increases energy output but if there are too many thinplates they are likely to break from physical shock and the battery fails.

Car batteries provide reliable, long life service and are able to provide acurrent of the order of 100 amperes so the starter motor can start the carengine. Liquid electrolyte makes it sensitive to orientation (doesn't workwell on its side or upside down!). Loses electric charge especially if onlypartly charged. Modern lead-acid batteries are sealed because antimonyin the lead prevents release of hydrogen and oxygen gas on recharging.

Battery lead is recycled.


Nickel-cadmium (Nicad) cell (1.2 V)

Lighter weight than lead-acid batteries but disposal of very toxiccadmium is of concern. Good high and low temperature performanceand very resistant to shock and vibration. Can be stored indefinitely inany state of charge but consistent overcharging reduces capacity (called'memory effect'). Cheapest rechargeable batteries available forphotoflash units, cordless power tools and older mobile phones and olderportable video cameras.

Ni (III) coated steel (cathode)

separator

cadmium (anode)

separator

in KOH electrolyte

Anode: Cd + 2OH– Æ Cd(OH)2 + 2e–

Cathode: Ni(III) + e– Æ Ni(II)

Lithium-MnO2 / Lithium ion (3.0V)

Button size (for calculators, watches and cameras) to lap-top computersize. High energy output for low mass but expensive.

MnO2 cathode

Li anode

Polymer electrolyteallows Li+ movementbut not e– movement

Li+

Anode: Li Æ Li+ + e–

Cathode: Mn(IV) + e– Æ Mn(III)


Flow batteries

Gaseous or liquid reductant and oxidant flow either side of a separatingmembrane. The development of suitable separating membranes is thegreatest challenge in this type of technology.

Fuel cell

Uses combustion redox reactions carried out without burning. Nocombustion pollutants are produced and up to twice as much electricalenergy is obtained compared with conventional production of electricityfrom combustion heat energy.

external circuit

anod

e

cath

ode

e– e–

O2H2CO3

2– CO2

H2O

molten carbonateelectrolyte

porous carbonelectrodes containing

metal catalysts

Anode: H2 + CO32– Æ H2O + CO2 + 2e–

Cathode: 1/2O2 + CO2 + 2e– Æ CO32–

Overall: H2 + 1/2O2 Æ H2O E = 1.2 V

Electrode membranes have short life and are expensive. A fuel cell can'tstore electricity the way other batteries do. Electrical energy is onlyreleased when the reactants flow and this requires pumping systems.


Zinc-air cell – a hybrid battery and fuel cell (1.25 V)

insulation

KOHelectrolyte

pastehydrophobic teflon layer

powdered zinc

steel can

seal removedfor air acess

The porous hydrophobic teflon polymer lets a flow of oxygen from theair in but keeps water out. This type has replaced many mercury buttoncells.

Vanadium redox cell (1.26 V)

About 3 M aqueous solutions of vanadium ions flow through a porousgraphite felt. Recharged by replacing the electrolyte solutions which canbe recycled. Recycling involves recharging, ideally using solar or windgenerated electrical energy.

pumppump

cathodeelectrolyte

vanadium (V)

anodeelectrolyte

vanadium (II)

electrolyte tankelectrolyte tank

cell stack(two cells)

externalcircuit

Anode: V(II) Æ V(III) + e–

Cathode: V(V) + e– Æ V(IV)

Invented by Professor Maria Skyllas-Kazacos at the University of NewSouth Wales, Sydney, Australia. Undergoing commercial development.


Gratzel cell (liquid junction photovoltaic device)

Photovoltaic devices such as silicon solar cells change intense solar lightenergy to electrical energy. Solar cells operating at 10% efficiency andcovering one thousandth of the earth's surface could totally satisfyhumanity's current energy needs.

Liquid junction photovoltaic devices work better in low intensity andchanging light situations and could be used as walls and windows ofbuildings.

The cell shown below was developed by Professor Michael Gratzel,Photonics Laboratory, Laussane, Switzerland.

organo-ruthenium dye

absorbed on

e–

I3– + 2e– 3I–

2Dye+ + 3I– 2Dye + I3–

2Dye 2Dye+ + 2e–e– e–

lightglass insulatortransparentconducting layer

semiconductor TiO2

e– e–

I– I3–

glass insulator

transparentconducting layer

e–

Exercise 4.1 at the end of this part gives some additional information aboutsome of these cells. To complete this exercise you are required to gather,process and present information to compare different types of cells.


Appendix

Table of standard potentials and half equations

oxidant + electron(s) reductant E (volts)

Li+ + e– Li –3.04

K+ + e– K –2.94

Ca2+ + 2e– Ca –2.87

Na+ + e– Na –2.71

Mg2+ + 2e– Mg –2.36

Al3+ + 3e– Al –1.68

H2O + e– 1/2H2(g) + OH– –0.83

Zn2+ + 2e– Zn –0.76

Fe2+ + 2e– Fe –0.44

Cd2+ + 2e– Cd –0.40

Ni2+ + 2e– Ni –0.24

Pb2+ + 2e– Pb –0.13

H+ + e– 1/2H2(g) 0.00

Cu2+ + 2e– Cu 0.34

1/2O2(g)+H2O + 2e– 2OH– 0.40

Cu+ + e– Cu 0.52

1/2I2(aq) + e– I– 0.62

Fe3+ + e– Fe2+ 0.77

Ag+ + e– Ag 0.80

1/2Br2(aq) + e– Br– 1.10

1/2O2(g)+2H+ + 2e– H2O 1.23

1/2Cl2(aq) + e– Cl– 1.40

1/2F2(g) + e– F– 2.89


Suggested answers

Metals and electrons1 Cu Æ Cu2+ + 2e–

2 Al Æ Al3+ + 3e–

3 2Mg + O2 Æ 2MgO

4 Mg + H2SO4 Æ MgSO4 + H2

5 Mg Æ Mg2+ + 2e–

6 2Al + 6HCl Æ 2AlCl3 + 3H2

7 Li Æ Li+ + e–

8 2H+ + 2e– Æ H2

9 2Li + 2H+ Æ 2Li+ + H2

Displacement of metals from solution1 The results show that when a metal is placed in a solution of its own

ions no reaction occurs.

2 The most reactive metal in this table is magnesium.

3 The least active metal in this table is silver.

4 An active metal reacts with less active metal ions.

5 The most reactive metal ion in this table is the silver ion.

6 The least reactive metal ion in this table is the magnesium ion.

7 If a metal atom is very reactive then its ion is much less reactive.


Observing reaction between iron atoms andcopper(II) ions1 c a solution of light green Fe2+ ions is oxidised by oxygen from the

air to yellow Fe3+ ions

b the part of the iron nail in the solution becomes thinner as ironatoms Fe dissolve to form light green iron(II) ions Fe2+

a the blue solution of copper(II) ions loses colour as blue Cu2+

ions react to form dark metallic copper Cu.

2 iron atoms + copper ions Æ iron ions + copper atoms

Fe + Cu2+ Æ Fe2+ + Cu

Oxidation/reduction reactions

Mg2+ + 2 e– Æ Mg RED

Zn2+ + 2 e– Æ Zn RED

Cu Æ Cu2+ + 2 e– OX

Cu2+ + 2 e– Æ Cu RED

Mg Æ Mg2+ + 2 e– OX

Ag Æ Ag+ + e– OX

Fe2+ + 2 e– Æ Fe RED

Pb2+ + 2 e– Æ Pb RED

Pb Æ Pb2+ + 2 e– OX

Zn Æ Zn2+ + 2 e– OX

Fe Æ Fe2+ + 2 e– OX

Ag+ + e– Æ Ag RED

a) redox stands for REDuction-OXidation

b) electron(s) are transferred from the chemical species that undergoesoxidation to the chemical species that undergoes reduction.


Oxidants and reductants

Reaction Oxidation Reduction Oxidant Reductant

Mg+Zn2+ ÆMg2++Zn Mg ÆMg2++2e– Zn2++2e– ÆZn Zn2+ Mg

Zn+Cu2+ ÆZn2++Cu Zn ÆZn2++2e– Cu2++2e– ÆCu Cu2+ Zn

Mg+2H+ ÆMg2++H2 Mg ÆMg2++2e– 2H++2e– ÆH2 H+ Mg

Zn Æ Zn2+ + 2e–

I2 + 2e– Æ 2I–

_________________

Zn + I2 Æ Zn2+ + 2I–

Oxidation state (oxidation number OxN)3 Mg + 2H+ Æ Mg2+ + H2

0 1 2 0 0 + 2 x 1 = 2 + 0

4 Mg + 2HCl Æ MgCl2 + H2

0 1 –1 2 –1 0 0 + 2 x (1–1) = 2+ (2 x –1) + 0

5 2Mg + O2 Æ 2MgO

0 0 2 –22 x 0 + 0 = 2 x (2–2)

Galvanic cells

Term Meaning

galvanise coat with zinc

voltage potential difference or electromotive force

voltmeter instrument measuring voltage

volt unit of potential difference or electromotive force

galvanometer instrument measuring small currents

voltameter measures quantity of electricity by decomposition


Investigating galvanic cells

To produce a galvanic cell the following are required:

• two different metals which cannot be touching

• an electrolyte solution (conducting solution) in which ions are free tomove and so conduct electric charge

• For a galvanic cell to provide a useful flow of electrons the twometals need to be connected by a conducting wire.

Electrodes

Low activity. More active metal electrodes could react with the water.

Measurement of standard potential

The table is labelled:

• ‘weak oxidants’ at the top left hand corner

• ‘strong oxidants’ at the bottom left hand corner

1 Ag + H+ Æ no reaction

2 Ni + 2Ag+ Æ Ni2+ + 2Ag

3 Na + H2O Æ Na+ + 1/2H2(g) + OH–

Primary (non-rechargeable batteries)

A lithium cell Li Æ Li+ + e– releases one mole of electrons fromabout 7 g (one mole) of lithium.

A zinc cell Zn Æ Zn2+ + 2e– releases one mole of electrons fromabout 33g of zinc.

The lithium cell is much lighter than a zinc cell.



Exercise 4.1 Name: _________________________________

Exercise 4.1: Comparing sources of electrochemicalenergy

Gather, process and present information to complete this table whichcompares five cells. Use the information provided in the section onSources of electrochemical energy.

Cell dry lead-acid button Lithium ion Vanadium

anode

cathode MnO2 MnO2 VO2+

electrolyte

EnergydensityW-h/kg

90 30 125 150 –

cost andpracticality

society andenvironmentimpact

Gill Sans Bold



Part 5: Nuclear chemistry


AMENDMENTS

111

Uuu –

Unu

nuni

um

1 H1.

008

Hyd

roge

n

3 Li6.

94Li

thiu

m

11 Na

22.9

9S

odiu

m

19 K39

.10

Pot

assi

um

37 Rb

85.4

7R

ubid

ium

55 Cs

132.

9C

aesi

um

87 Fr

[223

.0]

Fran

cium

4 Be

9.01

Ber

ylliu

m

12 Mg

24.3

1M

agne

sium

20 Ca

40.0

8C

alci

um

38 Sr

87.6

2S

tront

ium

56 Ba

137.

3B

ariu

m

88 Ra

[226

.0]

Rad

ium

21 Sc

44.9

6S

cand

ium

39 Y88

.91

Yttr

ium

57-7

1

LAN

THA

NID

ES

89-1

03

AC

TIN

IDE

S

22 Ti47

.87

Tita

nium

40 Zr

91.2

2Zi

rcon

ium

72 Hf

178.

5H

afni

um

104

Rf

[261

.1]

Rut

herfo

rdiu

m

23 V50

.94

Vana

dium

41 Nb

92.9

1N

iobi

um

73 Ta18

0.9

Tant

alum

105

Db

262.

1D

ubni

um

24 Cr

52.0

0C

hrom

ium

42 Mo

95.9

4M

olyb

denu

m

74 W18

3.8

Tung

sten

106

Sg

[263

.1]

Sea

borg

ium

25 Mn

54.9

4M

anga

nese

43 Tc[9

8.91

]Te

chne

tium

75 Re

186.

2R

heni

um

107

Bh

[264

.1]

Boh

rium

26 Fe

55.8

5Iro

n

44 Ru

101.

1R

uthe

nium

76 Os

190.

2O

smiu

m

108

Hs

[265

.1]

Has

sium

27 Co

58.9

3C

obal

t

45 Rh

102.

9R

hodi

um

77 Ir19

2.2

Iridi

um

109

Mt

[268

]M

eitn

eriu

m

28 Ni

58.6

9N

icke

l

46 Pd

106.

4P

alla

dium

78 Pt

195.

1P

latin

um

110

Uun –

Unu

nniliu

m

29 Cu

63.5

5C

oppe

r

47 Ag

107.

9S

ilver

79 Au

197.

0G

old

30 Zn

65.3

9Zi

nc 48 Cd

112.

4C

adm

ium

80 Hg

200.

6M

ercu

ry

112

Uub –

Unu

nbiu

m

5 B10

.81

Bor

on

13 Al

26.9

8A

lum

iniu

m

31 Ga

69.7

2G

alliu

m

49 In11

4.8

Indi

um

81 Tl

204.

4Th

alliu

m

113

6 C12

.01

Car

bon

14 Si

28.0

9S

ilicon

32 Ge

72.6

1G

erm

aniu

m

50 Sn

118.

7Ti

n

82 Pb

207.

2Le

ad

114

Uuq –

Unu

nqua

dium

7 N14

.01

Nitr

ogen

15 P30

.97

Pho

spho

rus

33 As

74.9

2A

rsen

ic

51 Sb

121.

8A

ntim

ony

83 Bi

209.

0B

ism

uth

115

8 O16

.00

Oxy

gen

16 S32

.07

Sul

fur

34 Se

78.9

6S

elen

ium

52 Te12

7.6

Tellu

rium

84 Po

[210

.0]

Pol

oniu

m

116

Uuh –

Unu

nhex

ium

9 F19

.00

Fluo

rine

17 Cl

35.4

5C

hlor

ine

35 Br

79.9

0B

rom

ine

53 I12

6.9

Iodi

ne

85 At

[210

.0]

Ast

atin

e

117

2 He

4.00

3H

eliu

m

10 Ne

20.1

8N

eon

18 Ar

39.9

5A

rgon

36 Kr

83.8

0K

rypt

on

54 Xe

131.

3X

enon

86 Rn

[222

.0]

Rad

on

118

Uuo –

Unu

noct

ium

57 La13

8.9

Lant

hanu

m

89 Ac

[227

.0]

Act

iniu

m

58 Ce

140.

1C

eriu

m

90 Th

232.

0Th

oriu

m

59 Pr

140.

9P

rase

odym

ium

91 Pa

231.

0P

rota

ctin

ium

60 Nd

144.

2N

eody

miu

m

92 U23

8.0

Ura

nium

61 Pm

[146

.9]

Pro

met

hium

62 Sm

150.

4S

amar

ium

94 Pu

[239

.1]

Plu

toni

um

63 Eu

152.

0E

urop

ium

95 Am

[241

.1]

Am

eric

ium

64 Gd

157.

3G

adol

iniu

m

96 Cm

[244

.1]

Cur

ium

65 Tb

158.

9Te

rbiu

m

97 Bk

[249

.1]

Ber

keliu

m

66 Dy

162.

5D

yspr

osiu

m

98 Cf

[252

.1]

Cal

iforn

ium

67 Ho

164.

9H

olm

ium

99 Es

[252

.1]

Ein

stei

nium

68 Er

167.

3E

rbiu

m

100

Fm

[257

.1]

Ferm

ium

69 Tm

168.

9Th

uliu

m

101

Md

[258

.1]

Men

dele

vium

70 Yb

173.

0Y

tterb

ium

102

No

[259

.1]

Nob

eliu

m

71 Lu17

5.0

Lute

tium

103

Lr[2

62.1

]La

wre

nciu

m

1 H1.

008

Hyd

roge

n

Ato

mic

num

ber

Sym

bol

Ato

mic

wei

ght

Nam

e

93 Np

[237

.0]

Nep

tuni

um

Part 5: Nuclear chemistry 1

Contents

Introduction ............................................................................... 2

Isotopes..................................................................................... 3

Uranium decay series ..........................................................................6

Detecting radiation .................................................................... 8

Balancing nuclear equations..............................................................10

Applications of radioisotopes................................................... 12

Nuclear reactors .................................................................................14

Production of transuranic elements...................................................16

Production of commercial radioisotopes ...........................................16


Exercises – Part 5 ................................................................... 23


Introduction

Nuclear chemistry provides a range of materials extensively used inmedicine, industry and scientific research.


• distinguish between stable and radioactive isotopes and describe theconditions under which a nucleus is unstable

• describe how transuranic elements are produced

• describe how commercial radioisotopes are produced

• identify instruments and processes that can be used to detectradiation

• identify one use of a named radioisotope

– in industry

– in medicine

• describe the way in which the above named industrial and medicalradioisotopes are used and explain their use in terms of theirchemical properties.


• process information from secondary sources to describe recentdiscoveries of elements

• use available evidence to analyse benefits and problems associatedwith the use of radioactive isotopes in identified industries andmedicine.




Isotopes

Isotopes are atoms of the same element that have different atomicmasses.

Mnemonic: 'iso' mean equal and the 'p' in isotope can be regarded asrepresenting protons. Isotopes all have the same number of protons andtherefore are all atoms of the same element. Isotopes differ in thenumber of neutrons and hence mass.

Any isotope can be represented by ZA E

A represents the mass number = number of protons + neutrons

Z represents the atomic number = number of protons

E represents the symbol of the element with atomic number Z.

ZA E can be used to represent an atom or a nucleus. If Z

A E represents anucleus the charge on the nucleus, Z+, is not shown separately.

Chemical reactions involve rearrangement of atoms while nuclearreactions involve the rearrangement of protons and neutrons in nuclei toform new nuclei and therefore new atoms.

Chemical reaction Nuclear reaction

atoms rearrange but don't change atoms of one element typically changeto atoms of another element

valence shell electrons are transferredor shared between atoms

protons and neutrons in a nucleus arerearranged or change in number

small amounts of energy involved large amounts of energy involved

rate affected by temperature, catalystand the type of compound an atom isin

rate affected by number of nuclei butnot by temperature, catalyst or type ofcompound a nucleus is in

no measurable change in mass measurable changes in mass


Of about 2000 isotopes that have been studied only 279 are stable! Mostisotopes are unstable and emit radiation as they spontaneously releaseenergy or decay. Each unstable isotope can be called a radioactiveisotope, radioisotope, radioactive nuclide or radionuclide. The timerequired for the radioactivity level to be halved is known as the half-life.

Half lives vary from less than a millionth of a second to more than a billionyears!

Complete this table of selected isotopes.

Isotopename

Isotopesymbol

Massno. A(p+n)

Atomicno. Z(p)

A – Z

(n)

Radio-activityemitted

Half-lifed=daysy=years

hydrogen-1 11H 1 1 0 – –

hydrogen-2or deuterium

12 H 2 1 1 – –

hydrogen-3or tritium

13 H 3 1 b 12.3 y

helium-4 ora-particle

24 He 4 2 – –

carbon-12 612 C 6 6 – –

carbon-14 614 C 14 8 b 5720 y

816 O – –

818O – –

cobalt-60 2760 Co 60 27 b, g 5.3 y

82206 Pb 82 – –

radon-222 86222 Rn 222 136 a, g 3.8 d

radium-226 88226 Ra 226 a, g 1622 y

uranium-235 92235 U 235 92 a, g 7x108 y

95241Am a, g 458 y

Check your answers.


Note that a or b emissions are often followed by a g emission. Emission

of an a or b particle produces a nucleus with a more stable proton to

neutron ratio. (Neutrons must be present in any nucleus containing morethan one proton. They are important in overcoming the repulsionbetween the positively charged protons close together in a nucleus).However there is often excess energy in the arrangement of neutrons andprotons after the a or b particle is emitted. Gamma rays are emitted as

the neutrons and protons rearrange to lower, more stable, energy levels.

Radiation emission occurs randomly. Which nucleus will decay nextcannot be predicted. Changes in temperature, pressure, chemical form(atom, molecule or ion), concentration. do not affect rate of decay. Rateof decay is measured by half-life, time for half the nuclei to decay.

Radiation Symbol Type Example of emission

alpha a24 Heparticle 88

226 Ra Æ 86222 Rn + 2

4 He

beta b-10 e particle 6

14 C Æ 714 N + -1

0 e

gamma g electromagneticradiation

2760 Co Æ 27

60 Co + g

An alpha particle consists of two protons and two neutrons and isequivalent to a helium nucleus 2

4 He.

A beta particle is usually a negative electron with negligible mass -10 e .

A gamma emission is a high frequency and therefore high energyelectromagnetic radiation pulse. Note that a new nucleus is not formed.

1 Complete the following radioactivity emissions by inserting 24 He, -1

0 eor g.

a) 1124 Na Æ 12

24 Mg +

b) 53131I Æ 54

131Xe +

c) 92238 U Æ 90

234 Th +

d) 1124 Na Æ 11

24 Na +

e) 1532 P Æ 16

32 S +


2 Complete the following sentences:

When an alpha particle or ____________ is emitted the nucleuschanges to that of a different element. Emission of a ____________lowers the energy level but does not produce a new nucleus.

Check your answers.

Uranium decay series

Uranium in nature consists of 99.3% 92238 U and 0.7% 92

235 U . Theseisotopes go though a series of decays to ultimately form stable leadisotopes. The uranium-238 decay series is shown below:

80 81 82 83 84 85 86 87 88 89 90 91 92 93Atomic number

202

206

210

214

218

222

226

230

234

238

242

Mas

s nu

mbe

r

U

Th

Ra

Rn

Po

Pb PoBi

Pb PoBiTl

Pb

U

Th Pa

The overall change is 92238 U Æ 82

206 Pb + 8 24 He+ 6 -1

0 e Note that:

• each a emission reduces atomic mass by 4 (loss of four nucleonsfrom the nucleus) and atomic number by 2 (loss of two protons)

• each b emission does not change atomic mass (mass of electron is

negligible compared to proton or neutron) but increases atomicnumber because a neutron changes to a proton and an electron:

01

11

10n p eÆ +-

• each step also emits at least one g ray (not shown in the diagrams),

and often more than one, as the neutrons and protons rearrange tolower energy levels.

• the 82206 Pb isotope is stable and thus does not emit radiation.


particle

Thorium 23490 protons

144 neutrons

Protactinium 23491 protons

143 neutrons

Diagram illustrating the b decay change 90234 Th Æ 91

234 Pa + -10 e

Radium 22688 protons

138 neutrons

Radon 22286 protons

136 neutrons

particle

Diagram illustrating the a decay change 88226 Ra Æ 86

222 Rn + 24 He

Complete the labelling of the uranium-235 decay series using symbols fromthe periodic table.

80 81 82 83 84 85 86 87 88 89 90 91 92 93Atomic number

203

207

211

215

219

223

227

231

235

239

243

Mas

s nu

mbe

r

Write an equation for the overall change

_________________________________________________________

Check your answers.


Detecting radiation

Emitted radiation interacts with the electrons in surrounding atoms.To measure the radioactivity of a sample these interactions are countedover time.

Alpha, beta and gamma emissions can be distinguished between bycomparing their penetrating power

(beta) particles

(alpha) particles

paper

aluminium (3 mm minimum)

lead (10 mm)

(gamma) rays

half (gamma)rays

quarter (gamma)rays

or paths in a magnetic field.

rays

particles

particlesN

S


The large alpha particles can only travel a few cm through air becausethey hit many atoms. This causes extensive ionisation (formation ofpositive ions and free electrons) in the air. Smaller beta particles cantravel about one metre in air and cause less ionisation. Gamma raystravel many metres through air and cause much less ionisation.

The penetrating distance is often measured for water because water is themain constituent of living organisms. On average alpha particlespenetrate about 0.03 mm (about the thickness of a single cell) betaparticles about 2 mm and gamma rays about 100 mm through water.

High energy radiation that causes emission of electrons from atoms iscalled ionising radiation and is potentially harmful to living things.Low energy radiation that only causes excitation of electrons to highershells is known as non-ionising radiation. Non-ionising radiation ismuch less likely to damage living things.

Radiation type

non-ionising ionising

lower energy higher energy

light emission ionisation to + ions and – electrons

detect with scintillation counter detect with Geiger-Muller counter

The main way of detecting ionisation is by a Geiger Muller tube.Radiation enters a thin window at the end of a sealed metal tubecontaining low pressure argon gas. The radiation ionises argon gasproducing electrons and positive ions which move to oppositely chargedelectrodes. The small pulse of electricity produced is amplified andcounted by attached electronic circuits.

negative electrode(metal tube)

positive electrode(wire)

pulse counter

mica window

argon gas atlow pressure

Geiger-Muller counter for high energy ionising radiation


Ionising radiation can also be detected by changes in silver halidecrystals in photographic film, discharge of electroscopes andcondensation of vapour to liquid in cloud chambers.

Radioactive emissions too weak to ionise surrounding atoms can bedetected by scintillation counters. A weak emission transfers energy toan atom by raising an electron to an outer energy level further from thepositive nucleus. When the electron in this excited atom drops back to alevel closer to the nucleus light is emitted. A photocell produces a pulseof electric current when hit by the light.

fluorescentsolute

molecule

solventmoleculeexcited

radioactivenucleus

energytransfer

radioactiveemission

liquid container

amplifierandpulsecounter

electronmultiplier couldproduce 106

electrons perphotoelectron

e–

focussingelectrodes

photomultiplier

photosensitivesurfaceemits electron

lightemission

Scintillation counter for low energy non-ionising radiation.

Certain solutions of organic molecules can dissolve radioactivebiological samples and emit light for each radioactive emission. Theamount of light emitted by the organic molecules is proportional to theamount of radioactivity emitted. This method is often preferred ininvestigating biological systems as higher energy ionising radiationwould form ions that can interfere with the normal chemistry of cells.

Balancing nuclear equations

A nuclear equation showing nuclear decay (emission of a,b or g) or

reaction between particles such as 92235 U + 0

1n Æ 92236 U must be balanced

• for mass (upper numbers) and

• for charge (lower numbers).


For 92235 U + 0

1n Æ 92236 U 235 + 1 = 236 and 92 + 0 = 92

For 01

11

10n p eÆ +- 1 = 1 + 0 and 0 = 1 + (–1)

For 92236 U Æ 56

141Ba + 3692 Kr + 3 0

1n 236 = 141 + 92 + 3 x 1 and 92 = 56 + 36 + 3 x 0

Therefore all these equations are balanced. As you do with chemicalequations, always check that an equation is balanced after it iscompleted.

Complete Exercise 5.1: Nuclear fission and Exercise 5.2: New elements.


Applications of radioisotopes

The chemical behaviour of a radioisotope is practically the same as thechemical behaviour of a non-radioactive isotope of the same element.

Radioactive tracers are radioisotopes used to signal the passage of anatom through a system.

In biological systems low energy emitting radioisotopes detectable byscintillation counters are often preferred to high energy emittingradioisotopes that could interfere with the biochemistry of the organisms.

Carbon-14 is a low energy beta emitter. If a plant is allowed tophotosynthesise in an atmosphere of carbon dioxide containing carbon-14, 14CO2, the chemical pathway followed by the carbon-14 is easilytraced. The 14CO2 is used by the plant in the same chemical ways asnormal carbon dioxide, 12CO2 .

Similarly radioactive hydrogen-3 (called tritium) can be used to trace thepathways of hydrogen in biological reactions.

Some elements have no suitable radioisotopes. For example the threeradioisotopes of oxygen have half-lives of the order of a minute sotheir radiation levels drop too rapidly for long term detection. Morecomplex and expensive equipment, a mass spectrometer, can be usedto separate isotopes according to mass but this technique and the effortrequired in preparing samples usually makes it less convenient thanusing radioisotopes.

The equation for photosynthesis is sometimes shown as6CO2 + 12H2

18O Æ C6H12O6 + 618O2 + 6H2O to emphasize that:

• the oxygen atoms in the oxygen gas come from water and not fromcarbon dioxide. The 6H2O on the RHS is ‘new’ water, formed from Oin the CO2 – it is not water from the LHS.• the mechanism for the reaction was understood using 18O isotope(which was traced by mass spectroscopy, not by radioactivity).


The most widely used radioisotope in medicine is technetium-99m.[The m after an isotope number indicates it is in a metastable state;energy is released as a g-ray when the isotope changes to a stable form99mTc Æ 99Tc + g ]. Technetium-99m is used in over half of all nuclear

medicine procedures because :

• the nucleus has a half-life of six hours which is long enough toinvestigate changes in a human body but minimises exposure toradiation

• the electronic structure can change to produce a number of oxidationstates. This enables production of a wide range of biologicallyactive chemicals. Different chemicals containing technetium-99mcan be made to target different body organs or tissues.

• low energy gamma rays emitted by the 99mTc cause little damage tothe body and are easily detected by a gamma ray sensitive camera.

Technetium-99m is produced in a generator consisting of a glass tubesurrounded by lead. The generator contains molybdenum-99 which isone of the products of nuclear fission in a nuclear reactor. The 99Mo,with a half life of 66 hours, changes to 99mTc which can be washed out ofthe molybdenum with a salt solution. The 99mTc is then chemicallyattached to a biological molecule which will concentrate in the targetedorgan.

Cobalt-60 is a g-emitter with a half life of just over 5 years. The cobalt is

in an inert (chemically unreactive) form inside a container designed toshield workers from its energetic gamma radiation. In industry 60Co hasa number of uses:

• gamma sterilisation of hospital supplies that would be damaged byheat sterilisation

• gamma sterilisation of food to destroy microorganisms thuspreventing spoilage and extending shelf life

• sterilisation of insect pests such as carpet beetles

• as a source of radiation to destroy cancer cells which are moresusceptible to radiation than ordinary cells

• detection of cracks and flaws in metal such as in castings and welds;the gamma radiation passing through the object is recorded on a filmjust as X-rays are recorded after passing through a human body

• as a radioactive source in automated thickness gauges.

Automatic thickness gauges use a gamma source such as Co-60 for thickmaterials.

A very thin material such as the plastic film produced below only needs aless penetrating source such as Sr-90.


bulk material

finished product

of suitable

thickness

meter

meter controls gapbetween rollers• closes gap when

reading high• opens gap when

reading low

beta radiation source

beta radiationdetector

Automated thickness gauge using a beta source.

Write a balanced equation for the a emission by Am-241.

(Used in house smoke alarms. Smoke absorbs ionisation produced in air byemitted a particles. The resultant reduction in current flowing through a

detector triggers the alarm.)_________________________________________________________

Check your answers.

Nuclear reactors

Approximately 25% of the world's electrical energy is generated fromheat energy released in nuclear reactors by nuclear fission of U-235.Nuclear fission is the division of a heavy nucleus into two unequalmasses. This is accompanied by emission of neutrons, gamma rays and alot of heat energy.

A nuclear reactor is a structure in which nuclear fission can becontrolled. The reactor consists of:

• nuclear fuel core

• coolant to cool the core and transfer heat to steam generators

• moderator to moderate the speed of neutrons so they can join U-235nuclei rather than bounce off

• control rods containing material that absorbs neutrons

• safety devices


• concrete containment shield to absorb neutrons and gamma rays.

pump

pump

steam generatorsteam producedturns turbine

generatorproduceselectricity

control rods

coolwatercondenser

water at high pressure

containment shell

reactorcore

reactorvessel

Natural uranium contains 0.7% U-235. Enrichment raises the U-235concentration to the 3-4% needed to maintain a chain reaction. In achain reaction for every neutron absorbed to cause a U-235 to fissionenough neutrons are emitted to cause another U-235 to fission. Thefission produces two or three neutrons and at least one of these needs tobe absorbed for the chain reaction to be sustained. The two unequal massnuclei are usually in the mass range 90-100 and 135-145. For example:

92235 U + 0

1n Æ 92236 U Æ 56

141Ba + 3692 Kr + 3 0

1n

The neutron rich environment inside a reactor core can be use to produce:

• transuranic elements with Z = 93, 94 and 95

• commercial radioisotopes for use in industry, medicine and chemicalresearch.

The most abundant uranium isotope U-238 does not undergo fission butcan be converted by neutron bombardment to U-239 which undergoesbeta decay to neptunium and plutonium:

92238 U + 0

1n Æ 92239 U Æ 93

239 Np + -10 e ; 93

239 Np Æ 94239 Pu + -1

0 e

Plutonium-239 is changed to Americium-241using neutronbombardment. Am-241 is used commercially in house smoke alarms.

94239 Pu + 0

1n Æ 94240 Pu ; 94

240 Pu+ 01n Æ 94

241Pu; 94241Pu Æ 95

241Am + -10 e


Production of transuranic elements

The elements with Z = 93, 94 and 95, that is, neptunium, plutonium andamericium, are produced by neutron bombardment in a nuclear reactor.

Transuranic elements with atomic numbers above 95 are produced usingparticle accelerators. Small charged atomic particles are accelerated tovery high speeds by using electrical attraction and repulsion. The smallparticles with high kinetic energy then hit a target of large atoms.

94239 Pu + 2

4 He Æ 96242 Cm + 0

1n

96242 Cm + 2

4 He Æ 98245Cf + 0

1n

Complete these equations for the production of transuranic elements:

1 99253 Es + 2

4 He Æ 101256 Md + _____

2 ____ + 612 C Æ 98

246 Cf + 4 01n

Check your answers.

Production of commercialradioisotopes

Separation of a particular element from the mixtures formed in nuclearfission in a reactor uses differences in chemical properties to separateelements. Used nuclear fuel also contains some unused U-235 which ischemically separated and recycled into new fuel rods.

Because nuclear reactors contain high speed neutrons they are ideal forproducing neutron rich isotopes. A neutron rich isotope contains moreneutrons in its nucleus than most other atoms of that element.

Cobalt-60, a gamma emitter, and strontium-90, a beta emitter, areneutron rich isotopes because their masses are above the atomic weightsfor cobalt and strontium of 58.9 and 87.6.

To make neutron deficient radioisotopes a cyclotron is used. Cyclotronsuse the same acceleration of positive particles as a linear accelerator buthave electromagnets so that the charged particles follow a spiral path.This makes the cyclotron compact enough to fit in a hospital basement.


The national medical cyclotron

Information about the National Medical Cyclotron at RPA Hospital inSydney run by the Australian Nuclear Science and Technology Organisation(ANSTO) is available through http://www.lmpc.edu.au/science.

Source: Hawkins, G. (Editor). (1992.) A nuclear source. AustralianNuclear Science and Technology Organisation. Figure 9.14


Knowing that neutron rich radioisotopes are reactor produced and neutrondeficient radioisotopes are cyclotron produced you should be able tocomplete the third column of this table. Use the periodic table on the insidecover of this module to help you decide

Radioisotope Use Reactor/cyclotron

technetium-99m imaging body parts reactor

iodine-131 treating thyroid disease

iodine-123 imaging thyroid gland

phosphorus-32 treating excess red blood cells

fluorine-18 studying brain function by PET

gallium-67 imaging tumours

Check your answer.

Complete Exercise 5.3: Radioisotopes.


Suggested answers

Isotopename

Isotopesymbol

Massno. A(p+n)

Atomicno. Z(p)

A – Z

(n)

Radio-activityemitted

half-lifed=daysy=years

hydrogen-111H 1 1 0 – –

hydrogen-2or

deuterium

12 H 2 1 1 – –

hydrogen-3or tritium

13 H 3 1 2 b 12.3y

helium-4 ora-particle

24 He 4 2 2 – –

carbon-126

12 C 12 6 6 – –

carbon-146

14 C 14 6 8 b 5720y

oxygen-168

16 O 16 8 8 – –

oxygen-188

18O 18 8 10 – –

cobalt-602760 Co 60 27 33 b, g 5.3y

lead-20682

206 Pb 206 82 124 – –

radon-22286

222 Rn 222 86 136 a, g 3.8d

radium-22688

226 Ra 226 88 138 a, g 1622y

uranium-235

92235 U 235 92 143 a, g 7x108y

americium-241

95241Am 241 95 146 a, g 458y


Isotopes

1. a) 1124 Na Æ 12

24 Mg + -10 e

b) 53131I Æ 54

131Xe + -10 e

c) 92238 U Æ 90

234 Th + 24 He

d) 1124 Na Æ 11

24 Na + g

e) 1532 P Æ 16

32 S + -10 e

2 When an alpha particle or beta particle is emitted the nucleuschanges to that of a different element. Emission of a gamma raylowers the energy level but does not produce a new nucleus.

Uranium decay series

Uranium-235 decay series

80 81 82 83 84 85 86 87 88 89 90 91 92 93Atomic number

203

207

211

215

219

223

227

231

235

239

243

Mas

s nu

mbe

r

U

ThAc

Rn

Po

Pa

Ra

Pb Bi

Tl Pb

Th

Overall equation is 92235 U Æ 82

207 Pb + 7 24 He+ 4 -1

0 e

Production of transuranic elements

1 99253 Es + 2

4 He Æ 101256 Md + 0

1n

2 92238 U + 6

12 C Æ 98246 Cf + 4 0

1n


Production of commercial radioisotopes

radioisotope use reactor/cyclotron

technetium-99m imaging body parts reactor

iodine-131 treating thyroid disease reactor

iodine-123 imaging thyroid gland cyclotron

phosphorus-32 treating excess red blood cells reactor

fluorine-18 studying brain function by PET cyclotron

gallium-67 imaging tumours cyclotron




Exercise 5.1 Nuclear fission

Combustion of a fossil fuel typically releases about 50 kJ per gram offuel.

Nuclear fission of uranium-235 releases much more energy.

92235 U + 0

1n Æ 92236 U Æ 56

141Ba + 3692 Kr + 3 0

1n + 2 x 1010 kJ

As for chemical equations the nuclear equation shows the energyreleased for mole quantities. One mole of U-235 releases about 2 x 1010

kJ of energy.

Calculate the energy released per gram of U-235 on nuclear fission. Setout your calculation showing working clearly.

Comment on the amount of energy released in a nuclear reaction (egfission) and the amount of energy released in a chemical reaction (egcombustion).

_________________________________________________________

_________________________________________________________


Exercise 5.2: New elements

Web sites vary enormously in the quality of the information provided.A chemistry site which has existed since 1993, is regularly updated, and ishighly regarded, can be found at:

http://www.webelements.com/index.html

This web site has a periodic table where you can get extensiveinformation on each element.

Use this web site to describe the recent discovery of two differenttransuranic elements.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________


Exercise 5.3: Radioisotopesa) Name a radioisotope used in medicine.

b) Briefly describe how this radioisotope is used.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

c) List up to three benefits and problems associated with use of thismedical radioisotope. Just use keywords or short phrases:

Benefits Problems

d) Name a radioisotope used in industry and identify (name) theindustry

e) Briefly describe how the radioisotope is used in this industry

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

f) List up to three benefits and problems associated with use of thisindustrial radioisotope. Just use keywords or short phrases:

Benefits Problems


f) What you have completed on the previous page could be brief noteswritten to help answer an extended response question.

‘Analyse the benefits and problems associated with the use of radioactiveisotopes. Include at least one medical radioisotope and one industrialradioisotope in your analysis.’

Analyse means 'draw out and relate implications'. Answer this extendedresponse question in the space below. Make sure you include half-life,radioactive waste disposal, security, human exposure to radiation andalternative ways of carrying out the activity in your answer.

Gill Sans Bold



Part 6: Review, report and outcomes


AMENDMENTS

111

Uuu –

Unu

nuni

um

1 H1.

008

Hyd

roge

n

3 Li6.

94Li

thiu

m

11 Na

22.9

9S

odiu

m

19 K39

.10

Pot

assi

um

37 Rb

85.4

7R

ubid

ium

55 Cs

132.

9C

aesi

um

87 Fr

[223

.0]

Fran

cium

4 Be

9.01

Ber

ylliu

m

12 Mg

24.3

1M

agne

sium

20 Ca

40.0

8C

alci

um

38 Sr

87.6

2S

tront

ium

56 Ba

137.

3B

ariu

m

88 Ra

[226

.0]

Rad

ium

21 Sc

44.9

6S

cand

ium

39 Y88

.91

Yttr

ium

57-7

1

LAN

THA

NID

ES

89-1

03

AC

TIN

IDE

S

22 Ti47

.87

Tita

nium

40 Zr

91.2

2Zi

rcon

ium

72 Hf

178.

5H

afni

um

104

Rf

[261

.1]

Rut

herfo

rdiu

m

23 V50

.94

Vana

dium

41 Nb

92.9

1N

iobi

um

73 Ta18

0.9

Tant

alum

105

Db

262.

1D

ubni

um

24 Cr

52.0

0C

hrom

ium

42 Mo

95.9

4M

olyb

denu

m

74 W18

3.8

Tung

sten

106

Sg

[263

.1]

Sea

borg

ium

25 Mn

54.9

4M

anga

nese

43 Tc[9

8.91

]Te

chne

tium

75 Re

186.

2R

heni

um

107

Bh

[264

.1]

Boh

rium

26 Fe

55.8

5Iro

n

44 Ru

101.

1R

uthe

nium

76 Os

190.

2O

smiu

m

108

Hs

[265

.1]

Has

sium

27 Co

58.9

3C

obal

t

45 Rh

102.

9R

hodi

um

77 Ir19

2.2

Iridi

um

109

Mt

[268

]M

eitn

eriu

m

28 Ni

58.6

9N

icke

l

46 Pd

106.

4P

alla

dium

78 Pt

195.

1P

latin

um

110

Uun –

Unu

nniliu

m

29 Cu

63.5

5C

oppe

r

47 Ag

107.

9S

ilver

79 Au

197.

0G

old

30 Zn

65.3

9Zi

nc 48 Cd

112.

4C

adm

ium

80 Hg

200.

6M

ercu

ry

112

Uub –

Unu

nbiu

m

5 B10

.81

Bor

on

13 Al

26.9

8A

lum

iniu

m

31 Ga

69.7

2G

alliu

m

49 In11

4.8

Indi

um

81 Tl

204.

4Th

alliu

m

113

6 C12

.01

Car

bon

14 Si

28.0

9S

ilicon

32 Ge

72.6

1G

erm

aniu

m

50 Sn

118.

7Ti

n

82 Pb

207.

2Le

ad

114

Uuq –

Unu

nqua

dium

7 N14

.01

Nitr

ogen

15 P30

.97

Pho

spho

rus

33 As

74.9

2A

rsen

ic

51 Sb

121.

8A

ntim

ony

83 Bi

209.

0B

ism

uth

115

8 O16

.00

Oxy

gen

16 S32

.07

Sul

fur

34 Se

78.9

6S

elen

ium

52 Te12

7.6

Tellu

rium

84 Po

[210

.0]

Pol

oniu

m

116

Uuh –

Unu

nhex

ium

9 F19

.00

Fluo

rine

17 Cl

35.4

5C

hlor

ine

35 Br

79.9

0B

rom

ine

53 I12

6.9

Iodi

ne

85 At

[210

.0]

Ast

atin

e

117

2 He

4.00

3H

eliu

m

10 Ne

20.1

8N

eon

18 Ar

39.9

5A

rgon

36 Kr

83.8

0K

rypt

on

54 Xe

131.

3X

enon

86 Rn

[222

.0]

Rad

on

118

Uuo –

Unu

noct

ium

57 La13

8.9

Lant

hanu

m

89 Ac

[227

.0]

Act

iniu

m

58 Ce

140.

1C

eriu

m

90 Th

232.

0Th

oriu

m

59 Pr

140.

9P

rase

odym

ium

91 Pa

231.

0P

rota

ctin

ium

60 Nd

144.

2N

eody

miu

m

92 U23

8.0

Ura

nium

61 Pm

[146

.9]

Pro

met

hium

62 Sm

150.

4S

amar

ium

94 Pu

[239

.1]

Plu

toni

um

63 Eu

152.

0E

urop

ium

95 Am

[241

.1]

Am

eric

ium

64 Gd

157.

3G

adol

iniu

m

96 Cm

[244

.1]

Cur

ium

65 Tb

158.

9Te

rbiu

m

97 Bk

[249

.1]

Ber

keliu

m

66 Dy

162.

5D

yspr

osiu

m

98 Cf

[252

.1]

Cal

iforn

ium

67 Ho

164.

9H

olm

ium

99 Es

[252

.1]

Ein

stei

nium

68 Er

167.

3E

rbiu

m

100

Fm

[257

.1]

Ferm

ium

69 Tm

168.

9Th

uliu

m

101

Md

[258

.1]

Men

dele

vium

70 Yb

173.

0Y

tterb

ium

102

No

[259

.1]

Nob

eliu

m

71 Lu17

5.0

Lute

tium

103

Lr[2

62.1

]La

wre

nciu

m

1 H1.

008

Hyd

roge

n

Ato

mic

num

ber

Sym

bol

Ato

mic

wei

ght

Nam

e

93 Np

[237

.0]

Nep

tuni

um

Part 6: Review, report and outcomes 1

Contents

Introduction ............................................................................... 2

Key ideas .................................................................................. 4

Suggested answers................................................................... 7

Exercises – Part 6 ................................................................... 11


Introduction

In this part you will review the first five parts of this module, report onyour open ended investigation and familiarise yourself with some of thesixteen outcomes designated for the HSC course. The HSC chemistrycourse outcomes are:

A student:

H1 evaluates how major advances in scientific understanding andtechnology have changed the direction or nature of scientificthinking

H2 analyses the ways in which model, theories and laws inchemistry have been tested and validated

H3 assesses the impact of particular advances in chemistry on thedevelopment of technologies

H4 assesses the impacts of applications of chemistry on society andthe environment

H5 describes possible future directions of chemical research

H6 explains reactions between elements and compounds in terms ofatomic structures and periodicity

H7 describes the chemical basis of energy transformations inchemical reactions

H8 assesses the range of factors which influence the type and rate ofchemical reactions

H9 describes and predicts reactions involving carbon compounds

H10 analyse stoichiometric relationships

H11 justifies the appropriateness of a particular investigation plan.

H12 evaluates ways in which accuracy and reliability could beimproved in investigations

H13 uses terminology and reporting styles appropriately andsuccessfully to communicate information and understanding


H14 assesses the validity of conclusions from gathered data andinformation

H15 explains why an investigation is best undertaken individually orby a team

H16 justifies positive values about and attitude towards both theliving and non-living components of the environment, ethicalbehaviour and a desire for critical evaluation of theconsequences of the applications of science.



H1 to H5 are Prescribed Focus Area outcomes

H6 to H10 are Knowledge and Understanding outcomes

H11 to H15 are Skills outcomes

H16 is a Values and Altitudes outcome

All outcomes except H16 could be assessed in the HSC Examination.


Key ideas

Assess your understanding of this module by answering these true/falsestatements one part at a time. Write T or F at the end of each statement.Approximately half the statements are true. If you decide the statementis false, rewrite the statement so that it is true.

Polymers from fossil fuels• Ethylene can be readily transformed into useful products because of

the reactivity of its double bond.

• Catalytic cracking of low value petroleum fractions to higher valuepetrol produces ethylene as a by-product.

• Alkanes and alkenes have high BPs because they are non-polar andhave weak dispersion forces between their molecules.

• The double bond in ethene makes it less reactive than ethane.

• Polyethylene is a commercially and industrially important additionpolymer formed from ethylene.

• High density polyethylene has more side branching than low densitypolyethylene.

• -(CH2CH)-n is polystyrene. | Cl

• most hydrocarbons except ethylene are used as fuels.

• most ethylene is used as a raw material to make other chemicals.

• addition polymers are formed from monomers with C=C bonds.

Polymers from biomass• Cellulose is a condensation polymer and a major constituent of

biomass.

• Cellulose contains short chains of carbon atoms.

• Cellulose is a protein biopolymer.


• Cellulase is a glucose based biopolymer.

• The human digestive system contains enzymes to digest cellulosebut not starch.

• Sugars in biomass can be converted to ethanol by yeast enzymes.

• Distillation to separate ethanol from mixtures of ethanol and waterrequires energy.

• When a biopolymer undergoes hydrolysis to produce glucose, wateris also produced.

• Starch and cellulose are condensation polymers of glucose withdifferent molecular structures.

• Sulfuric acid, phosphoric acid and heated ceramic solids can be usedto catalyse conversions between ethanol and ethylene.

Renewable ethanol• Ethanol reacts with water to form ethylene.

• Ethanol is able to dissolve many substances because it hashydrophilic and hydrophobic parts in its molecule.

• Fermentation of sucrose C12H22O11 to ethanol needs yeast enzymesand water.

• The molar heat of combustion would be higher for methanol CH3OHthan other alkanols.

• Ethylene would be regarded as a renewable resource if made fromcarbohydrates in plant biomass but as a non-renewable resource ifmade from hydrocarbons in fossil fuels.

• Combustion of alkanols is normally less polluting than combustionof hydrocarbons.

• C6H12O6 + H2O Æ 2C2H5OH + 2CO2

• C2H5OH Æ C2H4 + H2O

• C2H5OH + 3O2 Æ 2CO2 + 3H2O

• DcH is measured in kJ g–1.

Galvanic cells – electrical energy frommaterials• In Mg + Sn2+ Æ Mg2+ + Sn the reductant is Sn2+

• An oxidant undergoes reduction.

• The anode is where oxidation occurs in an electric cell.


• The anode of a battery is marked – .

• F2 is a strong oxidant.

• F– is a weak reductant.

• A metal of low activity will displace a more active metal from asolution of its salt.

• In the Daniell cell Zn | Zn2+ || Cu2+ | Cu electron flow is fromcopper to zinc.

• Electrons can flow through metal wires and aqueous electrolytesolutions.

• Photovoltaic devices change electrical energy to light energy.

Nuclear chemistry• Isotopes always have the same mass number.

• Radioactive isotopes are stable isotopes.

• Most transuranic elements have been produced using neutrons innuclear reactors.

• Neutron-deficient radioisotopes can be made in cyclotrons.

• a particles are more penetrating than b particles.

• High energy radioactivity causes ionisation of atoms.

• Low energy radioactivity is detected by scintillation counters.

• 3890 Sr Æ 39

90 Y is an example of b decay.

• 4399m Tc Æ 43

99 Tc is an example of a decay.

• 88226 Ra Æ 86

222 Rn is an example of g decay.


Suggested answers

Polymers from fossil fuels• Ethylene can be readily transformed into useful products because of

the reactivity of its double bond. T

• Catalytic cracking of low value petroleum fractions to higher valuepetrol produces ethylene as a by-product. T

• Alkanes and alkenes have high BPs because they are non-polar andhave weak dispersion forces between their molecules. F

Alkanes and alkenes have low BPs

• The double bond in ethylene makes it less reactive than ethane. F

The electron rich double bond in ethene makes it more reactive thanethane.

• Polyethylene is a commercially and industrially important additionpolymer formed from ethylene. T

• High density polyethylene has more side branching than low densitypolyethylene. F

High density polyethylene has less side branching so its moleculescan fit closer together and so have high density.

• -(CH2CH)-n is polystyrene. F Structure shown is PVC | poly(vinyl chloride) Cl

• most hydrocarbons except ethylene are used as fuels. T

• most ethylene is used as a raw material to make other chemicals. T

• addition polymers are formed from monomers with C=C bonds. T

Polymers from biomass• Cellulose is a condensation polymer and a major constituent of

biomass. T

• Cellulose contains short chains of carbon atoms. T


• Cellulose is a protein biopolymer. F

Cellulose is a glucose based biopolymer.

• Cellulase is a glucose based biopolymer. F

Cellulase is an enzyme and therefore a protein biopolymer.

• The human digestive system contains enzymes to digest cellulosebut not starch. F

The human digestive system contains enzymes to digest starch butnot cellulose.

• Sugars in biomass can be converted to ethanol by yeast enzymes. T

• Distillation to separate ethanol from mixtures of ethanol and waterrequires energy. T

• When a biopolymer undergoes hydrolysis to produce glucose, wateris also produced. F

When a biopolymer undergoes hydrolysis to produce glucose, wateris required as a reactant.

• Starch and cellulose are condensation polymers of glucose withdifferent molecular structures. T

• Sulfuric acid, phosphoric acid and heated ceramic solids can be usedto catalyse conversions between ethanol and ethylene. T

Renewable ethanol• Ethanol reacts with water to form ethylene. F

Ethylene reacts with water in the presence of catalyst to formethanol

• Ethanol is able to dissolve many substances because it hashydrophilic and hydrophobic parts in its molecule. T

• Fermentation of sucrose C12H22O11 to ethanol needs yeast enzymesand water. T

• The molar heat of combustion would be higher for methanol CH3OHthan other alkanols. F

Methanol contains fewer C and H atoms to be changed to CO2 andH2O releasing heat than do the other, larger alkanols.

• Ethylene would be regarded as a renewable resource if made fromcarbohydrates in plant biomass but as a non-renewable resource ifmade from hydrocarbons in fossil fuels. T

• Combustion of alkanols is normally less polluting than combustionof hydrocarbons. T

• C6H12O6 + H2O Æ 2C2H5OH + 2CO2 F

C6H12O6 Æ 2C2H5OH + 2CO2


• C2H5OH Æ C2H4 + H2O T

• C2H5OH + 3O2 Æ 2CO2 + 3H2O T

• DcH is measured in kJ g–1. F

DcH is the molar heat of combustion and so is measured in kJ

mol–1

Galvanic cells – electrical energy from materials• In Mg + Sn2+ Æ Mg2+ + Sn the reductant is Sn2+ F

The reductant is Mg.

• An oxidant undergoes reduction. T

• The anode is where oxidation occurs in an electric cell. T

• The anode of a battery is marked – . T

• F2 is a strong oxidant. T

• F– is a weak reductant. T

• A metal of low activity will displace a more active metal from asolution of its salt. F

A metal of higher activity will displace a less active metal from asolution of its salt.

• In the Daniell cell Zn | Zn2+ || Cu2+ | Cu electron flow is fromcopper to zinc. F

Electron flow is from the more active Zn to the less active Cu.

• Electrons can flow through metal wires and aqueous electrolytesolutions. F

Electrons can flow through metal wires but not through aqueouselectrolyte solutions. Movement of ions allows flow of electricitythrough aqueous electrolyte solutions.

• Photovoltaic devices change electrical energy to light energy. F

Photovoltaic devices change light energy to electrical energy.

Nuclear chemistry• Isotopes of an element always have the same mass number. F

Isotopes of an element always have the same atomic number butdifferent mass numbers.

• Radioactive isotopes are stable isotopes. F

Radioactive isotopes are unstable isotopes.


• Most transuranic elements have been produced using neutrons innuclear reactors. F

Transuranic elements with atomic numbers 93, 94 and 95 were madeusing neutron bombardment in nuclear reactors but the highertransuranic elements (up to atomic number 118) have been producedusing acceleration of positive ions in accelerators.

• Neutron-deficient radioisotopes can be made in cyclotrons. T

• a particles are more penetrating than b particles. F

a particles are less penetrating than b particles although they do

cause more ionisation.

• High energy radioactivity causes ionisation of atoms. T

• Low energy radioactivity is detected by scintillation counters. T

• 3890 Sr Æ 39

90 Y is an example of b decay. T

• 4399m Tc Æ 43

99 Tc is an example of a decay. F

This is g decay as there is no change in atomic number or mass

number.

• 88226 Ra Æ 86

222 Rn is an example of g decay. F

This is a decay as the atomic number has decreased by two and the

mass number has decreased by four.

Complete Exercise 6.1: Report on open ended investigation, Exercise 6.2:Skills outcomes and Exercise6.3: Prescribed focus area outcomes.




Exercise 6.1 Report on the open ended investigation

Part A: Use information resources to find the solubility of purechemicals in ethanol


Report on the open ended investigation (continued)

Part B: Use chemicals you have at home and test their solubility inmethylated spirits.


Exercise 6.2: Skills outcomes

In exercise 6.1 you were given an opportunity to demonstrate the skilloutcome H13: uses terminology and reporting styles appropriatelyand successfully to communicate information and understanding.

In this exercise you will be given an opportunity to demonstrate skilloutcomes H11, H12 and H14 by answering questions based on yourexperiences in completing the open ended investigation.

H11: justifies the appropriateness of a particular investigation plan

1 List data sources (information resources) used in Part A

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Devise a way of showing which data sources gave qualitative dataand which sources gave quantitative (measurement) data.

_____________________________________________________

3 The dependent variable is what you are interested in measuring.Independent variables are quantities that could affect the value of thedependent variable measurement.From your activity in Part B identify a dependent variable and anindependent variable and justify your choices.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

4 List a sequence of procedures used in your Part B activity.

_____________________________________________________

_____________________________________________________

_____________________________________________________


5 Give an example of where repetition of procedures is appropriate inPart B.

______________________________________________________

______________________________________________________

______________________________________________________

6 Identify a potential hazard in carrying out Part B.

______________________________________________________

______________________________________________________

______________________________________________________

7 How did you address the potential hazard?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

8 What technology did you use or could you have used in Part A orPart B?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

9 Was the method you used in Part B destructive or non-destructivetesting of a material's solubility? Justify (support your argument orconclusion in) your answer.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________


H12: evaluates ways in which accuracy and reliability could beimproved in investigations

1 Describe careful and safe disposal of waste materials produced bythe investigation in Part B.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Identify a safe work practice used during the investigation.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

H14: assesses the validity of conclusions from gathered data andinformation

1 Justify a conclusion from your investigation.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Formulate a cause and effect relationship to explain some of yourresults.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________


Exercise 6.3 Prescribed Focus Area outcomes

Complete the following tasks designed to give you familiarity with thePrescribed Focus Area Outcomes.

H1: evaluates how major advances in scientific understanding andtechnology have changed the direction or nature of scientificthinking

Evaluate means 'determine the value of '. Evaluate the impact ofGalvani's and Volta's work on biology, chemistry, physics andtechnology:

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

H3: assesses the impact of particular advances in chemistry on thedevelopment of technologies

Assesses means 'makes a judgment of the value of '. Assess the impactof Volta's work on development of technologies.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________


H4: assesses the impacts of applications of chemistry on society andthe environment

Assess the development of stable sources of electricity on society and theenvironment.

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

H5: describes possible future directions of chemical research

Describe possible future directions of chemical research for:

a) producing fuels from biomass

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) developing batteries

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

c) identifying the origin of chemicals in a human fingernail.

_____________________________________________________

_____________________________________________________

_____________________________________________________

CHEHSC 43071 The production of materials

Student evaluation of module

Name: ________________________ Location: ______________________

We need your input! Can you please complete this short evaluation toprovide us with information about this module. This information willhelp us to improve the design of these materials for future publications.

1 Did you find the information in the module clear and easy tounderstand?

_____________________________________________________

2 What did you most like learning about? Why?

_____________________________________________________

_____________________________________________________

3 Which sort of learning activity did you enjoy the most? Why?

_____________________________________________________

_____________________________________________________

4 Did you complete the module within 30 hours? (Please indicate theapproximate length of time spent on the module.)

_____________________________________________________

_____________________________________________________

5 Do you have access to the appropriate resources? eg a computer, theinternet, scientific equipment, chemicals, people that can provideinformation and help with understanding science

_____________________________________________________

_____________________________________________________

Please return this information to your teacher, who will pass it along tothe materials developers at OTEN – DE.

Learning Materials ProductionOpen Training and Education Network – Distance Education

NSW Department of Education and Training

production of materials - millennium schools production of materials chemical knowledge,...

Documents